Math lesson plan · 9th grade (Year 10 in England) · 45 minutes
Find both axis intercepts of Ax + By = C (cover-up method)
Algebra
CCSS HSA.CED.A.2CCSS HSF.IF.B.4England: GCSE Foundation Algebra
Objective and success criteria
Students will: Find both axis intercepts of Ax + By = C (cover-up method).
- 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: Read the slope and intercept from Ax + By = C
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 (Read the slope and intercept from Ax + By = C). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- What is the slope (gradient) of the line −2x − 2y = −8? → -1Prompt: Rearrange into y = mx + b.
- Find the slope of 6x − 4y = −8. Give a fraction in its simplest form. → 3/2 (1 1/2)Prompt: Get y on its own.
- At what y-value does −6x + 2y = −8 cross the y-axis? → -4Prompt: On the y-axis, 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 both axis intercepts of Ax + By = C (cover-up method). 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: Find the y-intercept of 2x − y = 6. Type it like (4, 0).
- Step 1: −y = 6 → y = −6
- Step 2: (0, −6)
- Answer: (0, −6)
- 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.
- Find the y-intercept of −x − 2y = 6. Type it like (4, 0). → (0, −3)Prompt: On the y-axis, x = 0.
- Elena sketches −x + 8y = 8 by joining its two intercepts. What is the area of the triangle formed by the line and the two axes? → 4Prompt: Find where the line meets each axis.
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.
- Find the x-intercept of 5x + y = 5. Type it like (4, 0). → (1, 0)Prompt: On the x-axis, y = 0.
- Omar sketches 7x + 3y = 21 by joining its two intercepts. What is the area of the triangle formed by the line and the two axes? → 10.5Prompt: Find where the line meets each axis.
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: Read the slope and intercept from Ax + By = C.
- 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-9.
Free lesson plan from eurekami.com/lesson-plan-builder