Math lesson plan · 8th grade (Year 9 in England) · 45 minutes
Find where a line crosses the x-axis
Algebra
CCSS 8.F.B.4England: KS3 AlgebraEngland: GCSE Foundation Algebra
Objective and success criteria
Students will: Find where a line crosses the x-axis.
- 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: Find the y-intercept from an equation, table or graph
Leads to: the next skill in this area.
Materials: Balance scales or a balance drawing, Algebra tiles, Function machine cards, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Find the y-intercept from an equation, table or graph). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- What is the y-intercept of y = −5 − 4x? → -5Prompt: The y-intercept is the value of y when x = 0.
- x: 1, 2, 3, 4. y: 0, −1, −2, −3. The pattern is linear. What is the y-intercept? → 1Prompt: Work out how much y changes when x goes up by 1.
- What is the y-intercept of y = x + 11? → 11Prompt: The y-intercept is the value of y when x = 0.
Hook · 5 min
- Show a "think of a number" puzzle and ask the class to work out the starting number.
- Share the objective: Find where a line crosses the x-axis. Read the success criteria together.
I do: model it · 10 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: Where does y = −x + 4 cross the x-axis? Give the x-value.
- Step 1: −x = −4
- Step 2: x = 4
- Answer: 4
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- Where does y = −4x − 12 cross the x-axis? Give the x-value. → -3Prompt: On the x-axis, y = 0.
- For 5x + 5y = 100, find the x-intercept. → 20Prompt: At the x-intercept, y = 0.
You do: independent practice · 10 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 · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- Where does y = −x + 1 cross the x-axis? Give the x-value. → 1Prompt: On the x-axis, y = 0.
- For 5x + 2y = 40, find the x-intercept. → 8Prompt: At the x-intercept, y = 0.
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: Find the y-intercept from an equation, table or graph.
- 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
- 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