7sin(2x)+7sin(x)=0

Divide every term by 7









sin(x) = 0;   2cos(x)+1 = 0
                 cos(x) = 
                   

If your problem states in the interval from 0° to 360°,
the answer is  0°,180°, 120°,240°

If your problem states in the interval from 0 to 2π,
the answer is  0,π,2π/3,4π/3 

If your problem states for all x in degrees, 
the answer is  180n°, 120°+360n°, 240180°+360n180°

If your problem states for all x (in radians), 
the answer is  n*π, 2π/3+2n*π, 4π/3+2n*π

Edwin