(sinx)tanx + sinx = 0 or sinx(tanx + 1) = 0
So, the expression = 0 when either sinx = 0 or when tanx + 1 = 0
from 0 to 2pi, sinx is zero when the angle is 0o or 180o (and pi multiples)
and when tanx = -1 results when the tanx is negative (+sinx & -cosx or -sinx & +cosx )
This occurs in the 2nd and 4th quadrant when the angle is 135o and 315o. (and pi multiples)