Half Angle Formula - Practice Questions & MCQ

Half Angle Formula

These formulae can be derived from the reduction formulas and we can use when we have an angle that is half the size of a special angle.

Note that the half-angle formulas are preceded by a ± sign. This does not mean that both positive and negative expressions are valid. Rather, only one sign needs to be taken and that depends on the quadrant in which α/2 lies.

The half-angle formula for sine is derived as follows:

To derive the half-angle formula for cosine, we have

For the tangent identity, we have