Math lesson plan · 10th grade (Year 11 in England) · 45 minutes
Evaluate composite functions f(g(a))
Algebra
CCSS HSF.BF.A.1.CEngland: GCSE Higher Algebra
Objective and success criteria
Students will: Evaluate composite functions f(g(a)).
- 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: Function notation
Leads to: Write the rule for a composite function
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 (Function notation). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- f(x) = 3x² − 4x − 1. Find f(5). → 54Prompt: Replace every x with 5.
- f(x) = −4x + 1. For what value of x is f(x) = −3? → x = 1Prompt: Set the expression equal to the value.
- f(x) = x² + 5x + 9. Find f(4). → 45Prompt: Replace every x with 4.
Hook · 5 min
- Show a "think of a number" puzzle and ask the class to work out the starting number.
- Share the objective: Evaluate composite functions f(g(a)). 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: f(x) = −3x + 4 and g(x) = x² − 2. Find g(f(−4)).
- Step 1: f(−4) = 16
- Step 2: g(16) = 254
- Answer: 254
- 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.
- f(x) = 3x − 2 and g(x) = x² + 6. Find f(g(2)). → 28Prompt: Work from the inside out.
- x: 1, 2, 3, 4, 5 f(x): 2, 4, 1, 3, 5 g(x): 5, 3, 2, 4, 1 Find f(g(2)). → 1Prompt: Read g(2) from the table first.
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.
- f(x) = x + 4 and g(x) = x² + 1. Find g(f(0)). → 17Prompt: Work from the inside out.
- x: 1, 2, 3, 4, 5 f(x): 2, 5, 1, 3, 4 g(x): 2, 1, 4, 5, 3 Find f(g(2)). → 2Prompt: Read g(2) from the table 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: Function notation.
- 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 the rule for a composite function.
- 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-10.
Free lesson plan from eurekami.com/lesson-plan-builder