Prove the identity. tan (tan 0 + cot 0) = sec 20 To verify the identity, work each side separately until you obtain the same expression. Start with the left side. Choose the correct step and transform the expression according to the step chosen. tan 0(tan 0+ cot 0) = = = sec 20 Multiply by a form of 1. Multiply by a form of 1. Distribute. Add.