SOHCAHTOA (right-angled trigonometry)
Sin = Opposite/Hypotenuse, Cos = Adjacent/Hyp, Tan = Opposite/Adjacent.
Right-angled trig links sides and angles. Pick the ratio that uses your two known quantities. Year 9 introduces; GCSE Foundation requires fluency.
Worked examples
sin 30° = 0.5, cos 60° = 0.5, tan 45° = 1.
If opposite = 5, hypotenuse = 10, then sinθ = 0.5 ⇒ θ = 30°.
If adjacent = 4, θ = 60°, then opposite = 4 × tan 60° ≈ 6.93.
Frequently asked questions
How do I remember which ratio?
SOHCAHTOA: Sin = Opp/Hyp, Cos = Adj/Hyp, Tan = Opp/Adj.
Calculator in degrees?
Yes for KS3. Make sure your calculator is in DEG mode (often shown as D in the display).