Math lesson plan · 10th grade (Year 11 in England) · 45 minutes
Trigonometric ratios: SOH CAH TOA
Trigonometry
CCSS HSG.SRT.C.6CCSS HSG.SRT.C.8England: GCSE Foundation GeometryEngland: GCSE Higher Geometry
Objective and success criteria
Students will: Trigonometric ratios: SOH CAH TOA.
- 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: Pythagoras' theorem; Similar shapes
Leads to: Pythagoras and trigonometry in 3D; Find angles with inverse trig; Exact trig values (0°, 30°, 45°, 60°, 90°)
Materials: Scientific calculators, Protractors and rulers, Right-triangle diagrams, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Pythagoras' theorem; Similar shapes). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Triangles ABC and DEF are similar. AB = 3 cm, BC = 6 cm and DE = 4.5 cm. Find EF in cm. → 9Prompt: Find the scale factor from the matching sides AB and DE.
- Triangles ABC and DEF are similar. AB = 5 cm, BC = 4 cm and DE = 20 cm. Find EF in cm. → 16Prompt: Find the scale factor from the matching sides AB and DE.
- Triangles ABC and DEF are similar. AB = 9 cm, BC = 10 cm and DE = 27 cm. Find EF in cm. → 30Prompt: Find the scale factor from the matching sides AB and DE.
Hook · 5 min
- Show a ramp or a ladder against a wall and ask how steep it is.
- Share the objective: Trigonometric ratios: SOH CAH TOA. 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: A ramp rises at 64° over a horizontal distance of 10 m. How high does it rise? Give 1 decimal place.
- Step 1: 10 × tan 64° = 20.503
- Step 2: ≈ 20.5 m
- Answer: 20.5
- 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.
- A ramp rises at 19° over a horizontal distance of 25 m. How high does it rise? Give 1 decimal place. → 8.6Prompt: You know the adjacent side and want the opposite: use tan.
- A ramp rises at 20° over a horizontal distance of 22 m. How high does it rise? Give 1 decimal place. → 8Prompt: You know the adjacent side and want the opposite: use tan.
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.
- A ramp rises at 44° over a horizontal distance of 6 m. How high does it rise? Give 1 decimal place. → 5.8Prompt: You know the adjacent side and want the opposite: use tan.
- A ramp rises at 51° over a horizontal distance of 15 m. How high does it rise? Give 1 decimal place. → 18.5Prompt: You know the adjacent side and want the opposite: use tan.
Watch out for
- Mixing up opposite and adjacent sides.
- Calculator in radians instead of degrees.
Support and stretch
Support
- Review first: Pythagoras' theorem.
- Use concrete materials: scientific calculators.
- 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: Pythagoras and trigonometry in 3D; Find angles with inverse trig; 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-10.
Free lesson plan from eurekami.com/lesson-plan-builder