# Verify the Identity cos(-x)-sin(-x)=cos(x)+sin(x)

Start on the left side.
Since is an even function, rewrite as .
Since is an odd function, rewrite as .
Multiply .
Because the two sides have been shown to be equivalent, the equation is an identity.
is an identity
Verify the Identity cos(-x)-sin(-x)=cos(x)+sin(x)