Start on the left side.

Rearrange terms.

Apply pythagorean identity.

Apply the reciprocal identity to .

Apply the product rule to .

One to any power is one.

Cancel the common factor of .

Cancel the common factor.

Rewrite the expression.

Because the two sides have been shown to be equivalent, the equation is an identity.

is an identity

Verify the Identity cos(x)^2(1+tan(x)^2)=1