Question

How do you solve `cos theta(sin theta-3cos theta)=0`?

Answer 1

Divide by cos x (condition: cos x not 0, x not `+- pi/2`)

`cos x(sin x/cos x - 3 cos x/cos x) = 0`

`tan x - 3 = 0 -> tan x = 3 = tan 71.57`

x = 71.57 deg

x = 71.57 + 180 = 251.59 deg