Formulas and rules
Every key math formula and rule, organised by topic and school level, with examples and study tips.
Trigonometry 4
SOH CAH TOA
sin = O/H ; cos = A/H ; tan = O/A
In a right triangle these ratios link an angle to two sides.
Exact trigonometric values
sin 30 = 1/2, cos 30 = sqrt3/2, tan 45 = 1
Common angles 0, 30, 45, 60, 90 have exact values worth memorising.
Pythagorean identity
sin^2 x + cos^2 x = 1
This identity holds for every angle.
Sine and cosine rules
a/sin A = b/sin B ; c^2 = a^2 + b^2 - 2ab cos C
Use the sine rule for pairs of side and angle, the cosine rule for three sides or two sides and the included angle.