1) The equality is wrong.
I am having trouble with some of these questions:
1. 2 tan (5pi/8) = tan 5pi/4 (use the double angle formula, but what is the answer)?
2. Express tan in terms of cosine and sine.
Do I use the Pythagorean identity? (1 + tan^2x = sec^2x and 1 + cot^2x = cot^2x)