Pythagoras and trigonometry
Lesson 5 of 14
Trigonometric ratios
Objective. Use sine, cosine and tangent to find sides and angles.
The key idea
Label the sides opposite, adjacent and hypotenuse relative to the angle, then choose the ratio containing the two sides you care about.
Worked example
Find x where the angle is 35° and the hypotenuse is 12, with x opposite.
- 1sin 35° = x / 12.
- 2x = 12 × sin 35°.
Answer: x ≈ 6.88
Practice
Each question comes with a picture and a listen button. Try it first, then reveal the answer.
Common mistake. Leaving the calculator in radians during a degrees question.
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