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)##