How do you verify the identity sin(pi/2 + x) = cosx?

for the true proof you need to use matrice but this is acceptable :
##sin(a+b) = sin(a)cos(b)+cos(a)sin(b)##
##sin(pi/2+x) = sin(pi/2)*cos(x)+cos(pi/2)*sin(x)##
##sin(pi/2) = 1##
##cos(pi/2) = 0 ##
So we have :
##sin(pi/2+x) = cos(x)##