Math lesson plan · 9th grade (Year 10 in England) · 30 minutes
Simplify surds (radicals)
Number sense
CCSS HSN.RN.A.2England: GCSE Higher Number
Objective and success criteria
Students will: Simplify surds (radicals).
- 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: Square roots and cube roots; Prime factorisation
Leads to: Rationalise the denominator; The quadratic formula; Exact trig values (0°, 30°, 45°, 60°, 90°)
Materials: Place value chart, Base-ten blocks or a number line, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 4 min
- Quick retrieval from earlier learning (Square roots and cube roots; Prime factorisation). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- What is ∛1000? → 10Prompt: Which number, used three times in a multiplication, gives this?
- Which is 150 written as a product of prime factors? (2 × 3² × 5 / 3 × 5² / 2 × 3 × 5² / 2² × 3 × 5²) → 2 × 3 × 5²Prompt: Keep dividing by the smallest prime that works (2, 3, 5, 7…).
- √74 lies between which two whole numbers? (7 and 8 / 6 and 7 / 8 and 9 / 9 and 10) → 8 and 9Prompt: List the square numbers near it.
Hook · 3 min
- Show a number in the news or a price tag and ask what each digit is worth.
- Share the objective: Simplify surds (radicals). Read the success criteria together.
I do: model it · 7 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: Simplify √80. It can be written as k√5. What is k?
- Step 1: √80 = √(16 × 5)
- Step 2: = √16 × √5
- Step 3: = 4√5
- Answer: 4
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 6 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- Simplify √175. It can be written as k√7. What is k? → 5Prompt: Look for the largest square number that divides it.
- Work out √12 × √3. → 6Prompt: √a × √b = √(ab).
You do: independent practice · 7 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 6 questions are on the student sheet below, with answers in the key.
Exit ticket · 3 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- Simplify √180. It can be written as k√5. What is k? → 6Prompt: Look for the largest square number that divides it.
- Simplify √32 + √2. Write it as k√2; what is k? → 5Prompt: Simplify each surd first.
Watch out for
- Reading 1,045 as one thousand four hundred five: point to each place and say its value.
- Thinking a longer number is always bigger, even with decimals (0.45 vs 0.5).
Support and stretch
Support
- Review first: Square roots and cube roots.
- Use concrete materials: place value chart.
- 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: Rationalise the denominator; The quadratic formula; Exact trig values (0°, 30°, 45°, 60°, 90°).
- 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