Answer:
See below.
Explanation:
4 cos x / tan x + 15 = 0
tan x = sin x / cos x so substituting:
4 cos x / sin x / cos x + 15 = 0
4 cos^2 x / sin x + 15 = 0
4 ( 1 - sin^2 x) / sin x + 15 = 0
Multiplying through by sin x :
4 - 4 sin^2 x + 15 sin x = 0
Multiply through by -1:
4 sin^2 x - 15 sin x - 4 = 0.