Utilise les formules de d'additions :
cos(a+b) = cos(a)cos(b) - sin(a)sin(b)
cos(a-b) = cos(a)cos(b) + sin(a)sin(b)
sin(a+b) = sin(a)cos(b) + cos(a)sin(b)
sin(a-b) = sin(a)cos(b) - cos(a)sin(b)
exemple pour le A
A = cos(x - pi/2)
A = cos(x)cos(pi/2) + sin(x)sin(pi/2)
A = sin(x)