7.5 Lines and Planes in 3D Space: Mathematics Communication

So far, you have focused on written mathematical language. In this section, you will practise understanding and taking part in spoken mathematical discussions and written email exchanges. You will read and analyse a dialogue between two students, and an email correspondence between four students.

The goal of this section is not just to understand the dialogue and the email, but to help you feel confident in having similar discussions and writing emails yourself. You will learn how to have a discussion about mathematics, ask and answer questions, and explain your ideas clearly to someone else. This will help you use English for practical conversations about mathematics, both in class and out of class. To do this, you will need to:

  • notice useful phrases and sentence structures in the dialogues,

  • memorise them,

  • practise saying them,

  • and finally, use them in real conversations.

Each line in the dialogues is numbered to help you talk about specific parts easily. For example, if you have a question, you can say: What does the second word from the end of line 8 mean?

By working with these texts, you will improve your ability to discuss mathematics in English, ask and answer questions, and communicate your ideas clearly with others.

Dialogue 1: two students

An example dialogue between two university students, Luke and Callum, who have arranged to work together for a while, sitting together in a study space, discussing lines and planes in three-dimensional space.

Select the ‘Play’ button to watch the video. The activities are based on the dialogue below the video.

Line Speaker Conversation
(1) Luke: Oh, hi Callum. How are you doing?
(2) Callum: Yeah, all good here, by and large. We're going to look at lines and planes in three dimensions today, right? How are you by the way?
(3) Luke: Yeah, pretty good. Although I’ll be better when I’ve got this stuff locked down. On which note, I've started the chapter, and I'm finding it quite hard to visualise. In 2D, a line is fairly straightforward, but in three dimensions things get a bit more abstract.
(4) Callum: Yeah, you’re right, it can get tricky. The fundamentals are the same. In 2D we can uniquely determine a line using two points passing through it. We can also define the line using a point passing through it and a vector along it. It is the same idea in 3D, the only difference is that we have one more coordinate.
(5) Luke: So given a point and a direction vector, I can define a line that extends infinitely in both directions along that vector.
(6) Callum: Exactly! This is called the parametric representation. Think of the point being your starting point, and the parameter measures how far along the line you are from your starting point. Of course, for the parameter to measure the actual distance, the vector must be a unit vector.
 (7) Luke: Unit vector?
(8) Callum: That’s just a vector that has length, or magnitude, one.
 (9) Luke: Ohhh I see, that makes sense.
(10) Callum: Now, here’s where 3D differs from 2D. In 2D, two lines either intersect or are parallel. But in three dimensions, two lines can either intersect, be parallel and not intersect, or not be parallel and not intersect.
(11) Luke: Ah that’s what skew lines are, right? Two lines that do not intersect and are not parallel. And how about planes?
 (12) Callum: That’s right. To define a plane in 3D, you specify a point on the plane and a vector perpendicular to the plane.
 (13) Luke: Is that what we call the normal vector? How does that work?
 (14) Callum: Exactly! Imagine the plane as a flat surface, like a sheet of paper. The normal vector is a vector that points straight up at right angles to every direction on the plane. Any point on the plane can be described in terms of our starting point and the normal vector.
 (15) Luke: So, how can I find the equation of the plane, using this?
 (16) Callum: Any vector within the plane must be perpendicular to the normal vector. So their dot product will be zero. Because remember from the chapter on vectors, that the dot product of perpendicular vectors is zero.
 (17) Luke: Ah yes! I can see in the lecture notes all the details. And, what can we do with the equation of the plane, once we calculate it?
(18) Callum: Well, you can find the distance from a point to the plane, or where a line intersects the plane. You can also find the line where two planes intersect. All of these involve concepts from the chapter of vectors.
(19) Luke: I see, I should definitely go back and revise vectors then.
(20) Callum: Oh yes, vectors are fundamental to understanding 3D geometry.
(21) Luke: Thank you very much, Callum. This is starting to feel much less abstract now!
(22) Callum: You're welcome! Once you practise a few problems, it'll become even clearer.

 

Activity 1: True, False, Unknown

From the options below, decide which statements are True, which are False and which are Unknown. in relation to the text.

(Note: If you believe a statement is mathematically true, but the information is not provided in the dialogue, you must select Unknown).

Next, select the ‘Answer’ button below the options.

Statement 1: Luke is fairly comfortable working with lines in just two dimensions but is finding the generalisation to 3D space more challenging.

Statement 2: There are fewer ways for two lines to relate to each other in 3D space than there are in 2D space.

Statement 3: A point on a plane can be defined using a starting point and a normal vector.

Statement 4: A normal vector that points in the exact opposite direction can be used to calculate a point on the plane in the exact same way.

Answers

Statement 1 is True. Luke explicitly states this in Line 3: In 2D, a line is fairly straightforward, but in three dimensions things get a bit more abstract.

Statement 2 is False. The passage contradicts this. In Line 10, Callum explains that in 2D, two lines have two possible relationships (they intersect or are parallel). In 3D, there are three possible relationships (intersect, parallel, or skew/not parallel and not intersecting). Therefore, there are more ways for lines to relate in 3D, not fewer.

Statement 3 is True. Callum states this directly in Line 14: Any point on the plane can be described in terms of our starting point and the normal vector.

Statement 4 is Unknown in relation to the text. Mathematically, this statement is true (if [latex]\mathbf{n}[/latex] is a normal vector, then [latex]\mathbf{-n}[/latex] is also a normal vector to the same plane). However, this specific detail is not mentioned anywhere in the text.

Activity 2: The language of explanation

In mathematical discussions, explanations are often built step-by-step across several sentences. Each sentence has a specific function (a job that it does to help build understanding).

Consider line (4) from the dialogue, repeated below. In this extract, Callum responds to Luke's comment that in three dimensions things get a bit more abstract. The sentences have been numbered in square brackets [1] to [4] for convenience.

The fundamentals are the same. [1] In 2D we can uniquely determine a line using two points passing through it. [2] We can also define the line using a point passing through it and a vector along it. [3] It is the same idea in 3D, the only difference is that we have one more coordinate. [4]

Here is an analysis of the function of each sentence in Callum's explanation:

  • [1] A statement that lines in 2D and 3D space are identical at the most basic level.
  • [2] A definition of a line in 2D.
  • [3] A second, complementary definition of a line in 2D, using a single point and a vector.
  • [4] A generalisation of the definitions in [2] and [3] to 3D. This serves as a summary statement and echoes the statement in [1].

Your task: Now consider two other multi-sentence explanations that Callum gives, specifically sections (10) and (14). Re-read each extract below and make a note of the function of each sentence, following the pattern shown above. You may need to look at the surrounding context of each extract. Next, select the 'Answer' button below to compare your notes with the suggested analysis.

(10) Now, here’s where 3D differs from 2D. [1] In 2D, two lines either intersect or are parallel. [2] But in three dimensions, two lines can either intersect, be parallel and not intersect, or not be parallel and not intersect. [3]

(14) Exactly! [1] Imagine the plane as a flat surface, like a sheet of paper. [2] The normal vector is a vector that points straight up at right angles to every direction on the plane. [3] Any point on the plane can be described in terms of our starting point and the normal vector. [4]

Answer

Here is an analysis of the function of each sentence in the two extracts. (Note: Your own descriptions may use different words, but the general meaning should be similar.)

Extract (10):

  • [1]: In the context of the previous comments between Luke and Callum, this sentence introduces a contrast by stating that 2D and 3D lines differ from each other.
  • [2]: This sentence sets up the first part of the contrast by giving two properties of 2D lines.
  • [3]: This sentence completes the contrast, using But, by stating the three possible properties of 3D lines.

Extract (14):

  • [1]: This single word sentence affirms that Luke's previous question in (13) (Is that what we call the normal vector?) was correct.
  • [2]: Using the instructional verb imagine, this sentence offers a physical, metaphorical definition of a plane to help with visualisation.
  • [3]: Building on the definition of the plane in [2], this sentence provides a definition of the normal vector.
  • [4]: Assuming the information given in [2] and [3], this final sentence explains how to define any point on the plane.

Language Focus: informal language for expressing understanding

In the dialogue, Luke uses several useful expressions to talk about his learning progress and his understanding of the mathematics. Some of these are listed below:

  1. I’ll be better when I’ve got this stuff locked down. Meaning: when I have fully mastered or memorised this material.

  2. … and I'm finding it quite hard to visualise. Meaning: difficult to picture in my mind.

  3. I should definitely go back and revise vectors then. Meaning: review and study previous material.

  4. It's starting to feel much less abstract now. Meaning: feeling more concrete, practical, and easier to understand.

Working with a partner, take turns asking and answering the following questions about your own experiences studying mathematics. Try to use Luke's expressions in your answers.

  1. Tell me about a time when you really got a difficult topic in mathematics locked down. How did you achieve it?
  2. Are there any aspects of mathematics that you find quite hard to visualise?
  3. What topics do you feel you should definitely go back and revise at the moment?
  4. Tell me about a time when an aspect of mathematics started to feel less abstract for you. What helped it click?

Activity 3: Your turn!

Goal

Practise having conversations about lines and planes in 3D space in English. Focus on communication, not necessarily on solving new math problems.

Set-up

In pairs, take the following roles:

Speaker A is the student that has a question about a problem in lines and planes in 3D. Speaker A can either choose something that is an actual problem, or something that they already understand and pretend they don't.

Speaker B is the student that has the answer to the question and needs to explain it to Speaker A.

 

Procedure

Step 1: Assign the roles - one student takes Speaker A and the other student takes Speaker B.

Step 2: Decide a problem from the topic of lines and planes in 3D to discuss.

Step 3: Take 3 to 5 minutes to look over the dialogue above and note down any useful phrases.

Step 4: Run the dialogue. Speaker A should start, either with a variation on Luke's opening above, or with something else, for example, Hi [Speaker B]. Do you have a quick moment to help me out with [Problem P]. It shouldn't take more than a couple of minutes. 

Step 5: Switch roles and practise again to experience both asking and answering.

Step 6: Together reflect on what went well. You might reflect on how accurately and fluently the dialogue was produced, how confident you felt, and if there are alternative ways of going through the dialogue.


Email Correspondence: Organising group work

Below is an example email correspondence between four university students, Aisha Patel, Jamal Hassan, Chen Wei and Sofia Rodriguez discussing the organisation of some group work.

Email Number Email
(1)

From: a.patel@northbury.edu.ac.uk
To: j.hassan@northbury.edu.ac.ukc.wei@northbury.edu.ac.uks.rodriguez@northbury.edu.ac.uk
Subject: Group work for Lines and Planes in 3D Space assignment

Hello everyone,

I hope you're all doing well. I'm getting in touch to organise our group work for the lines and planes assignment. We need to complete four problems covering lines, planes, intersections, and distances.

Could we meet sometime next week to divide up the work and go through the assignment together? I'm fairly flexible with timing. What works best for everyone?

Also, do you think we should meet in person or use Teams?

Cheers,
Aisha

(2)

From: c.wei@northbury.edu.ac.uk
To: a.patel@northbury.edu.ac.ukj.hassan@northbury.edu.ac.uks.rodriguez@northbury.edu.ac.uk
Subject: RE: Group work for Lines and Planes in 3D Space assignment

Hey Aisha,

Thanks for reaching out! I'm happy to work on this together. I think Tuesday or Wednesday next week would work well for me. I'd prefer to meet in person if possible! I find it easier to work through 3D geometry problems when we can draw diagrams together.

What topics are the four problems covering? That might help us decide how to split the work fairly.

Best,
Chen

(3)

From: s.rodriguez@northbury.edu.ac.uk
To: a.patel@northbury.edu.ac.ukj.hassan@northbury.edu.ac.ukc.wei@northbury.edu.ac.uk
Subject: RE: Group work for Lines and Planes in 3D Space assignment

Hi all,

I'm in! Tuesday or Wednesday works for me as well. I agree with Chen about meeting in person; drawing and visualising the 3D geometry will definitely help.

From what I've read, the four problems are: (1) finding the equation of a line given a point and direction; (2) finding the equation of a plane given three points; (3) finding the distance from a point to a plane; and (4) finding the line of intersection of two planes. Should we each take one problem?

See you next week,
Sofia

(4)

From: j.hassan@northbury.edu.ac.uk
To: a.patel@northbury.edu.ac.ukc.wei@northbury.edu.ac.uks.rodriguez@northbury.edu.ac.uk
Subject: RE: Group work for Lines and Planes in 3D Space assignment

Hi team,

Tuesday late afternoon works better for me than Wednesday, if that's okay with everyone. I'm a bit rusty on projections, so I'd actually like to pair up with whoever takes problem 3 (the distance from a point to a plane), since that uses projection concepts.

Otherwise, I'm happy to take problem 2 (equation of a plane) or problem 4 (intersection of two planes).

What are people's preferences?

Cheers,
Jamal

(5)

From: a.patel@northbury.edu.ac.uk
To: j.hassan@northbury.edu.ac.ukc.wei@northbury.edu.ac.uks.rodriguez@northbury.edu.ac.uk
Subject: RE: Group work for Lines and Planes in 3D Space assignment

Perfect! So Tuesday late afternoon works for everyone then. How about 5 PM in the maths common room?

For the work division, how about this:

  • Aisha and Jamal: Problem 3 (distance from a point to a plane) and Problem 4 (intersection of two planes)

  • Chen: Problem 1 (finding the equation of a line)

  • Sofia: Problem 2 (finding the equation of a plane)

Each person presents their solution, and we check each other's work. Does that sound fair?

I'll book the room and send you the booking confirmation.

See you Tuesday!

Aisha

(6)

From: c.wei@northbury.edu.ac.uk
To: a.patel@northbury.edu.ac.ukj.hassan@northbury.edu.ac.uks.rodriguez@northbury.edu.ac.uk
Subject: RE: Group work for Lines and Planes in 3D Space assignment

All agreed! Sounds like a solid plan. See you Tuesday at 5 PM.

Thanks for organising this, Aisha!

Cheers,
Chen

 

Activity 1: Global understanding

When reading a chain of emails, it is important to be able to step back from the details (like who is doing which problem) and understand the "big picture" or overall outcome of the correspondence.

From the options below, decide which summary you think most accurately describes the overall outcome and tone of the email exchange between the four students. Next, select the 'Answer' button below the options to check your understanding.

Option 1: Although the email exchange begins well with buy-in from all four students, problems arise and a collective decision cannot be reached.

Option 2: The group works well together to select a time and successfully agree on how to divide up the work.

Option 3: Two distinct opinions arise as to how to approach the group task but after some discussion, an overall decision is reached.

Option 4: The group works well together to establish a time, but they experience difficulties around how to divide up the work.

 

Answer

Option 2 is the correct answer. Option 1 is not correct, as no problems arise throughout the email chain; all four students reply positively and constructively. Option 3 is not correct because there is never a "discussion" of distinct opinions regarding the workload. Aisha makes a single suggestion for the division of work in Email 5, and it is immediately accepted by the rest of the group in Email 6. Option 4 is not correct for the same reason as Option 3; the group does not experience any difficulties dividing the work. Jamal states his preferences clearly (Email 4), and Aisha successfully incorporates them into a plan (Email 5).

Activity 2: Identifying useful language 1

Activity 2.1: Emails are not face-to-face communication, so it is important to choose your language carefully to ensure the tone is appropriate for your audience.

The email chain you just read is interesting because it is between peers (students). Therefore, it uses more informal and relaxed language than an email to a lecturer would. Note: Communicative practices, including email, vary greatly across different cultures. The observations made in this activity are based on typical email practices in UK universities.

Consider three elements of (1), reproduced below for convenience:

  1. The address form (how the email starts).

  2. The sign-off (how the email ends).

  3. The use of positive language (words or phrases that build a friendly relationship or make a positive comment before discussing the task).

Re-read (1). Note down these three aspects and consider how formal or informal they are. Next, select the 'Answer' button below to compare your thoughts.

Hello everyone,

I hope you're all doing well. I'm getting in touch to organise our group work for the lines and planes assignment. We need to complete four problems covering lines, planes, intersections, and distances.

Could we meet sometime next week to divide up the work and go through the assignment together? I'm fairly flexible with timing. What works best for everyone?

Also, do you think we should meet in person or use Teams?

Cheers,
Aisha

 

Answer
  1. Address form: Hello everyone. This is considered a fairly neutral opening in contemporary UK emails. It is less formal than Dear all, but slightly more formal than Hi all or Hey guys.
  2. Sign-off: Cheers. This is very informal and friendly. In the UK, it is often used among students or close colleagues. It contrasts with more formal sign-offs (listed here in descending order of formality): Yours sincerelyKind regardsBest wishes, and Thanks.
  3. Positive language: I hope you're all doing well. This is a standard, polite opening phrase. Before asking her classmates to do work, Aisha uses this sentence to build a friendly connection. This is a very common feature of British email culture.

 

Activity 2.2:  In the previous activity, we saw how Aisha opened the email chain using friendly, semi-informal language. However, as an email conversation continues back and forth, the level of formality often changes.

Your task: Re-read the other emails (2) through (6) in the chain. For each email, note down:

  1. The address form (how the email starts).

  2. The sign-off (how the email ends).

  3. Any positive language (words or phrases that build a friendly relationship or show enthusiasm).

 

Answer
Email Address form Sign-off Positive language
(2) (Chen) Hey Aisha, …

Note that Chen addresses only Aisha, not the whole group. To include everyone, he could have said Hi Aisha and all.

Best, …

This is a standard, versatile sign-off (short for Best wishes).

Thanks for reaching out! I'm happy to work on this together.

Chen uses very enthusiastic, positive language before discussing the task.

(3) (Sofia) Hi all, …

Another informal greeting, but this time addressed to everyone.

See you next week, …

A standard, friendly sign-off for people you know you will see soon.

I'm in!

This short, informal phrase means I am very happy to participate in this. It shows strong enthusiasm.

(4) (Jamal) Hi team, …

Using the word team (instead of all or everyone) creates a positive sense of collaboration and shared goals.

Cheers, …

A very informal, friendly sign-off.

Arguably none. This email is fairly direct and focused on the task. However, Jamal does say "I'm happy to pair up", which softens his request.
(5) (Aisha) None. Aisha drops the formal greeting entirely. The word Perfect! acts as the opening. See you Tuesday!

This is a very informal and positive sign-off.

Perfect!

This is an enthusiastic way of saying that everything is agreed upon.

(6) (Chen) None. Like Email 5, Chen drops the greeting. The words All agreed! act as the opening.

Cheers, …

A brief, informal sign-off

All agreed! Sounds like a solid plan.

Thanks for organising this, Aisha!

The phrase solid plan means a very good, reliable plan. They also explicitly thank Aisha for her effort.

In general, the formality level decreases as the email thread continues. By emails (5) and (6), the writers stop using specific address forms (like Hi everyone) altogether and jump straight into the message. This is very common in UK email culture when people are replying quickly to a chain.

Reflection task: Think about your own email writing habits.

  • Are there any phrases that you overuse (e.g., always starting with Dear... even when replying to a friend)?

  • Could you vary your expressions more using the examples from this table?

  • Do you sometimes use language that might be too informal for a lecturer, or too formal for a classmate?

Activity 3: Identifying useful language 2

In addition to address forms, sign-offs, and positive language, the email chain contains several other useful functional phrases. These are the specific groups of words that students use to negotiate, suggest, and agree on plans.

Your task: Read the paraphrased meanings below. Go back to the email text and identify the exact phrase or sentence that matches each meaning. Once you have found the phrases, select the 'Answer' button below to check your answers and read the language notes.

  1. In (1), a phrase that explains why the writer is sending the email.
  2. In (1), a sentence that means something like I can meet at almost any time.
  3. In (2), an expression of preference for meeting face-to-face.
  4. In (3), a phrase which means something like As far as I've understood from the reading …
  5. In (4), a phrase which means something like I will need to revise topic X or I am not sure I remember everything about topic X
  6. In (5), a three-word phrase used to make a suggestion.
  7. In (6), two consecutive short sentences that mean something like That's decided! This arrangement will work. 

 

Answer
  1. I'm getting in touch to organise our group work… Language Note: To get in touch means to contact someone. Notice the grammatical structure: I am getting in touch + to (infinitive verb showing purpose). This is a very common, polite way to state the purpose of an email.
  2. I'm fairly flexible with timing. Language Note: Flexible is a useful adjective when organising meetings. It tells the other person that you are willing to adapt to their schedule.
  3. I'd prefer to meet in person if possible! Language Note: In person is the standard English phrase for "face-to-face". Also note the use of I'd prefer (I would prefer) and if possible. This softens the statement, making it a polite request rather than a demand.
  4. From what I've read,… Language Note: This is a great phrase for introducing information that you believe is correct, but want to politely check with the group. It is short form of Based on the information I have read...
  5. I'm a bit rusty on [topic X]… Language Note: Rusty literally describes old metal, but idiomatically it means you have forgotten how to do something because you haven't practised it recently. It is a natural way for a student to admit they need help or need to review a mathematical topic.
  6. … how about … Language Note: How about... is a classic structure for making a suggestion in English. It can be followed by a noun phrase (e.g., How about Tuesday?) or an '-ing' verb (e.g., How about meeting on Tuesday?).
  7. All agreed! Sounds like a solid plan. Language Note: All agreed confirms that a group consensus has been reached. A solid plan is an idiomatic way of saying a good, reliable, or well-thought-out plan. Note that the pronoun It has been dropped from the beginning of the second sentence ([It] sounds like a solid plan), which is common in informal written English.

Activity 4: Your turn!

You have read and analysed the email correspondence between the students organising a mathematics assignment. Now, it is your turn to practice writing emails of this kind.

Working in a group of 3 or 4, you will create a similar, imaginary email chain to organise a group presentation for a mathematics module.

Step 1: Before writing, discuss the following with your group:

  • What is the mathematical topic of your presentation? (e.g., Applications of integrationSolving linear systems using matrices).

  • Who will write the first email?

Step 2: The student whom the group chooses to write the first email should draft it and send it to the rest of the group. This email must include the following elements:

  1. An appropriate address form and a brief, polite introduction (e.g., checking in with the group).

  2. A description of the task you have decided upon (mentioning what needs to be done to prepare for the presentation).

  3. A question asking when the group is available to meet.

  4. An appropriate sign-off.

(Tip: Look back at Aisha's first email to help you structure this).

Step 3: Once the first email is sent, the other group members should reply to the thread. When writing your replies, try to use the polite and functional phrases you learned in the previous activities. For example:

  • Thanks for reaching out...

  • I'm fairly flexible with timing...

  • How about...

  • I'm a bit rusty on...

Continue replying to each other until you have agreed on a time to meet and successfully divided up the presentation tasks.

Step 4: When your email chain is complete, review it together. Did you manage to reach an agreement? How did the formality of your language change from the first email to the last?

 

In this section, you practised reading and performing a dialogue (spoken communication) about mathematics, and explored written communication through email correspondence. In the next section, you will focus on longer written mathematical texts.

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