Question

what is the value of π in trigonometry and what is Cos 90`

Answer 1

$2\pi=360^o\\\pi=180^o\\\cos90^o=\cos\frac\pi2=\sin(90^o-90^o)=\sin0^o=0$

Answer 2

In trigonometry,

π radians = 180°

And

cos 90° = 0