Math lesson plan · 9th grade (Year 10 in England) · 60 minutes
Factorise fully: common factor first, then the bracket
Algebra
CCSS HSA.SSE.A.2England: GCSE Higher Algebra
Objective and success criteria
Students will: Factorise fully: common factor first, then the bracket.
- 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: Take out the greatest common factor of a polynomial; Difference of two squares; Factorise quadratics x² + bx + 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 · 6 min
- Quick retrieval from earlier learning (Take out the greatest common factor of a polynomial; Difference of two squares; Factorise quadratics x² + bx + c). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Complete the factorisation: 30x⁵ + 42x⁴ − 36x³ = 6x³( … ). Type what goes inside the bracket. → 5x^2+7x-6Prompt: Divide each term by 6x³.
- Factorise: 9x² − 25 ((3x + 5)² / 3(x + 5)(x − 5) / (3x − 5)² / (3x + 5)(3x − 5)) → (3x + 5)(3x − 5)Prompt: This is a difference of two squares: A² − B² = (A + B)(A − B).
- Factorise: x² − 8x − 9 ((x − 8)(x + 1) / (x − 1)(x + 9) / (x − 9)(x + 1) / (x + 1)(x − 9)) → (x + 1)(x − 9)Prompt: Find two numbers that multiply to −9 and add to −8.
Hook · 6 min
- Show a "think of a number" puzzle and ask the class to work out the starting number.
- Share the objective: Factorise fully: common factor first, then the bracket. 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: Factorise fully: 2x² + 8x + 6
- Step 1: 2(x² + 4x + 3)
- Step 2: 2(x + 1)(x + 3)
- Answer: 2(x + 1)(x + 3)
- 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.
- Factorise fully: 3x² − 6x − 72 ((3x − 6)(x + 4) / 3(x² − 2x − 24) / (x − 6)(x + 4) / 3(x − 6)(x + 4)) → 3(x − 6)(x + 4)Prompt: Every coefficient is a multiple of 3: take it out first.
- Factorise fully: 3x² − 12 (3(x² − 4) / 3(x + 2)(x − 2) / 3(x − 2)² / (x + 6)(x − 2)) → 3(x + 2)(x − 2)Prompt: Take out the common factor.
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.
- Elena says x³ − 16x = x(x² − 16) is fully factorised. What is the full factorisation? (x²(x − 16) / x(x − 4)² / x(x + 4)(x − 4) / x(x² − 16)) → x(x + 4)(x − 4)Prompt: A bracket can often be factorised further.
- Factorise fully: 3x² − 108 (3(x − 6)² / (x + 18)(x − 6) / (3x + 6)(x − 6) / 3(x + 6)(x − 6)) → 3(x + 6)(x − 6)Prompt: Take out the common factor.
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: Take out the greatest common factor of a polynomial.
- 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