#1**+1 **

If cos(a) = 12/13, then the adjacent side is 12 and the hypotenuse is 13 (or a multiple of these).

If the adjacent side is 12 and the hypotenuse is 13, the opposite side is 5 (Pythagorean Theorem).

However, since the angle is in the 4^{th} quadrant, we'll have to make the opposite side = -5.

sin(2a) = 2·sin(a)·cos(a) = 2·(-5/13)·(12/13) = .......

cot(2a) = 1 / tan(2a) = 1 / (-5/12) = ........

geno3141 Jul 17, 2020