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)?

And ...

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)