If, like me, you have the graph of the functions burned into your memory, then the anti-symmetry of sin makes it's geometric interpretation easy to remember. S

If, like me, you have the graph of the functions burned into your memory, then the anti-symmetry of sin makes it's geometric interpretation easy to remember. Sin and Cos correspond to the rejection and projection of two unit vectors. When they rotate past each other, the projection still has the same direction, but the rejection changes sign, so it must correspond to the anti-symmetric sin, not the symmetric cos.