# Cosine and Sine Identities with Dihedral Transformations

Cosine and Sine Identities with Dihedral Transformations

The relation between certain cosine and sine identities and certain rotations and reflections in the plane are exhibited. For example, is the same as , which is the (90°) clockwise rotation, , of the point .

(cos(t+π/2),sin(t+π/2))

(-sin(t),cos(t))

π/2

(x,y)↦(-y,x)

(cos(t),sin(t))