Question

how do i work out sinx+2sinxcosx=0 in radians?

Answer 1

First factor out a sin(x)
$sin x (1 + 2cos x) = 0$
Now you can split it into factors, where each factor = 0 and solve them separately.
$sin x = 0 , 1 + 2cos x = 0$
$sin x = 0 , cos x = -\frac{1}{2}$
You can use the unit circle to find the appropriate angles:(attached)
sin x = 0 when
$x = 0, \pi$
cos x = -1/2  when 
$x = \frac{2 \pi }{3}, \frac{4 \pi }{3}$