Choose the ratio
A standard method from Trigonometry: the steps.
Steps
| Ratio | Uses | Memory |
|---|---|---|
| sin θ = opposite ÷ hypotenuse | SOH | |
| cos θ = adjacent ÷ hypotenuse | CAH | |
| tan θ = opposite ÷ adjacent | TOA |
- Mark the angle θ.
- Label the sides from θ's point of view: opposite (across from θ), adjacent (next to θ, not the hypotenuse), hypotenuse (across from the right angle).
- Circle the side you know and the side you want. Pick the ratio that uses both.
- Write the equation and solve. To find an angle, use sin⁻¹, cos⁻¹ or tan⁻¹.
Why it works: every right triangle with the same angle θ is similar, so the ratio of its sides is always the same number.
For the whole topic, read Trigonometry: key points, common mistakes and how the DSE tests it.