The half angle formulas are used to find the exact values of the trigonometric ratios of the angles like 22.5° (which is half of the standard angle 45°), 15° (which is half of the standard angle 30°), etc. Half-angles in half angle formulas are usually denoted by θ/2, x/2, A/2, etc and the half-angle is a sub-multiple angle.
As we know, the double angle formulas can be derived using the angle sum and difference formulas of trigonometry. Half angle formulas can be derived using the double angle formulas.
We study half angle formulas (or half-angle identities) in Trigonometry.
