[tex]\bf 2sin^2(\theta)+sin(\theta)=0\impliedby \textit{common factor}
\\\\\\
sin(\theta)[2sin(\theta)+1]=0\implies
\begin{cases}
sin(\theta)=0\\\\
\theta=sin^{-1}(0)\\
---------\\
2sin(\theta)+1=0\\\\
sin(\theta)=\frac{-1}{2}\\\\
\theta=sin^{-1}\left( -\frac{1}{2} \right)
\end{cases}[/tex]
check those angles with those values in your Unit Circle
