Verify the identity. 2 tan o tan 20 = 1 - tan a To verify the identity, start with the left side and transform it to look like the right side. Choose the correct transformations and transform the expression at each step. tan 2a = tan Rewrite as a sum of two angles. Rewrite as a quotient of two angles. Rewrite as a difference of three angles. Rewrite as a sum of three angles. Rewrite as a difference of two angles