Lesson Plan

• Describe the definitions of sine, cosine and tangent for right‑angled triangles.
• Apply Pythagoras’ theorem to find missing sides of right‑angled triangles.
• Use the sine rule to determine unknown sides or angles in any triangle.
• Calculate angles or sides using the cosine rule.
• Identify common errors when matching sides with angles.

• Projector or interactive whiteboard
• Printed worksheets with triangle diagrams
• Scientific calculators
• Rulers and protractors
• Quick‑reference handout of formulas
• Set of example problem cards

Start with the question, “How can we find the height of a tree without climbing it?” Recall that students already know the basic SOH‑CAH‑TOA ratios from previous work. Explain that today they will extend this knowledge to any triangle using the sine, cosine and Pythagoras rules and will be able to solve real‑world problems.

1. Do‑now (5'): Quick quiz on SOH‑CAH‑TOA and Pythagoras.
2. Mini‑lecture (10'): Review of trigonometric ratios, Pythagoras, sine rule and cosine rule with short worked examples projected.
3. Guided practice (15'): Students work in pairs on Example 1 and Example 2, teacher circulates to check understanding.
4. Independent practice (15'): Worksheet covering all four concepts; students solve problems individually.
5. Check for understanding (5'): Exit ticket – one problem requiring the sine rule.
6. Summary (5'): Recap key formulas and common pitfalls.

Summarise how the sine, cosine and tangent ratios, Pythagoras’ theorem, and the sine and cosine rules work together to solve any triangle. Collect the exit tickets to gauge mastery and assign a homework worksheet with mixed triangle problems for further practice.