Tom K. answered 11/01/20
Knowledgeable and Friendly Math and Statistics Tutor
3π/2 < u < 2π, so this is the fourth quadrant, with positive cos
sin(u) = -3/5, so cos is 4/5 (If a side is length 3 and the hypotenuse is 5, the other side is length 4)
sin(2u) = 2 sin(u)cos(u) = 2 (-3/5)(4/5) = -24/25
cos(2u) = 2 cos2(u) -1 = 2(4/5)2 - 1 = 32/25- 1 = 7/25
tan(2u) = sin(2u)/cos(2u) = -24/25/(7/25) = -24/7