Question

cos (pi/2 - x) = senx true or false

Answer 1

Sabemos que:

$\boxed{cos(a-b)=cosa*cosb+sena*senb}$

Então:

$cos(\frac{\pi}{2}-x) = cos\frac{\pi}{2}*cosx+sen\frac{\pi}{2}*senx\\\\\ cos(\frac{\pi}{2}-x)=0*cosx+1*senx\\\\ cos(\frac{\pi}{2}-x)=0+senx\\\\\ \boxed{cos(\frac{\pi}{2}-x)=senx}$

Portanto, é verdadeiro (is true).