Math lesson plan · 8th grade (Year 9 in England) · 60 minutes

Find the y-intercept from an equation, table or graph

Algebra

CCSS 8.F.B.4England: KS3 AlgebraEngland: GCSE Foundation Algebra

Objective and success criteria

Students will: Find the y-intercept from an equation, table or graph.

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: Write y = mx + b from a slope and intercept, or from a graph; Write a linear function rule from a table; Find where a line crosses the x-axis

Materials: Balance scales or a balance drawing, Algebra tiles, Function machine cards, Mini whiteboards and pens, Printed student sheet (below).

Warm-up · 6 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 (3, 9) lie on the line y = 4x − 5? (Yes / No) → NoPrompt: Substitute the x-value into the equation.
Does the point (1, −3) lie on the line y = 2x − 4? (Yes / No) → NoPrompt: Substitute the x-value into the equation.
Does the point (2, −10) lie on the line y = −3x − 5? (Yes / No) → NoPrompt: Substitute the x-value into the equation.

Hook · 6 min

Show a "think of a number" puzzle and ask the class to work out the starting number.
Share the objective: Find the y-intercept from an equation, table or graph. Read the success criteria together.

I do: model it · 12 min

Work through the example out loud, saying why you do each step, not just what you do.
Example: What is the y-intercept of y = 4x − 9?
Step 1: x = 0 → y = −9
Answer: -9
Pause after each step and ask a student to say what comes next.

We do: guided practice · 12 min

Do these together. Students try each step on whiteboards before you reveal it.
Use the hints as prompts rather than giving the answer.

What is the y-intercept of y = −12 + 3x? → -12Prompt: The y-intercept is the value of y when x = 0.
x: 1, 2, 3, 4. y: −3, −8, −13, −18. The pattern is linear. What is the y-intercept? → 2Prompt: Work out how much y changes when x goes up by 1.

You do: independent practice · 17 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 8 questions are on the student sheet below, with answers in the key.

Exit ticket · 7 min

Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

What is the y-intercept of y = 2x − 5? → -5Prompt: The y-intercept is the value of y when x = 0.
x: 1, 2, 3, 4. y: 6, 2, −2, −6. The pattern is linear. What is the y-intercept? → 10Prompt: Work out how much y changes when x goes up by 1.

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: Write y = mx + b from a slope and intercept, or from a graph; Write a linear function rule from a table; Find where a line crosses the x-axis.
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