(cosx-tanx)/(sinx+cosx)=cosx-secx

Question

Verify this triganomic identity you can only use 1 side to solve

Answer 1

First we need to check the identity. Let x=0 then:

(1-0)/(0+1)=1-1, which isn’t true because 1≠0, so the identity is false.

To confirm, let x=π/4:

(√2/2-1)/√2=√2/2-√2, (1-√2)/2≠-√2/2.

Therefore the identity has been wrongly stated. So the identity is actually an equation which has particular solutions for x. An identity has to be true for all x.