Can you help to prove this?

Question

(sinx+1)(sinx-1)=cotx*sinx-2cosx

Answer 1

The equation is NOT an identity.

 

(sinx+1)(sinx - 1) = sin²x - 1 = -cos²x

 

(cotx)(sinx) - 2sinx = (cosx/sinx)(sinx) - 2cosx = -cosx

 

-cos²x ≠ -cosx, in general