Question

Why would knowing the Pythagorean identity sin2x + cos2x = 1 and the sum identities allow you to prove all the other identities?

Answer 1

These are simple trigonometric identities.

Answer 2

If you divided each side by (sinx)(sinx), the result is 1+(cotx)(cotx)=(cscx)(cscx)


If you divide each side by (cosx)(cosx), the resut is 1+(tanx)(tanx)=(secx)(secx)


These are the basic trigonometric identities.