Math lesson plan · 8th grade (Year 9 in England) · 30 minutes
Find the equation of a line
Algebra
CCSS 8.F.B.4CCSS HSA.CED.A.2England: GCSE Foundation AlgebraEngland: GCSE Higher Algebra
Objective and success criteria
Students will: Find the equation of a line.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Graphs of linear equations y = mx + b
Leads to: Linear regression and correlation coefficient; Use point-slope form y − y₁ = m(x − x₁)
Materials: Balance scales or a balance drawing, Algebra tiles, Function machine cards, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 4 min
- Quick retrieval from earlier learning (Graphs of linear equations y = mx + b). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Does the point (−4, −18) lie on the line y = 4x − 2? (Yes / No) → YesPrompt: Substitute the x-value into the equation.
- Does the point (2, −7) lie on the line y = −3x − 3? (Yes / No) → NoPrompt: Substitute the x-value into the equation.
- Does the point (3, 14) lie on the line y = 3x + 4? (Yes / No) → NoPrompt: Substitute the x-value into the equation.
Hook · 3 min
- Show a "think of a number" puzzle and ask the class to work out the starting number.
- Share the objective: Find the equation of a line. Read the success criteria together.
I do: model it · 7 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: A line has slope −4 and crosses the y-axis at −8. Write its equation as y = … (type the right-hand side).
- Step 1: y = −4x − 8
- Answer: -4x-8
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 6 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- A line has slope 4 and crosses the y-axis at −7. Write its equation as y = … (type the right-hand side). → 4x-7Prompt: Use y = mx + b.
- Find the equation of the line through (1, −1) and (5, −9). Type the right-hand side of y = … . → -2x+1Prompt: Find the slope first.
You do: independent practice · 7 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 6 questions are on the student sheet below, with answers in the key.
Exit ticket · 3 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- A line has slope −5 and crosses the y-axis at −8. Write its equation as y = … (type the right-hand side). → -5x-8Prompt: Use y = mx + b.
- Find the equation of the line through (1, −1) and (5, −17). Type the right-hand side of y = … . → -4x+3Prompt: Find the slope first.
Watch out for
- Doing an operation to one side of an equation but not the other.
- Reading 3x as 3 + x, or thinking x always stands for one particular number.
Support and stretch
Support
- Review first: Graphs of linear equations y = mx + b.
- Use concrete materials: balance scales or a balance drawing.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Move on to: Linear regression and correlation coefficient; Use point-slope form y − y₁ = m(x − x₁).
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/math/grade-8.
Free lesson plan from eurekami.com/lesson-plan-builder