Question

How do you simplify `cos(x+pi/2)`?

Answer 1

Use the known trigonometric identity

`cos(a+b)=cosa*cosb-sina*sinb`

we have that

`cos(x+pi/2)=cosx*cos(pi/2)-sinx*sin(pi/2)=cosx*0-sinx*1=-sinx`

Finally

`cos(x+pi/2)=-sinx`