Solving $4\sin^2{x}\cos^2{x}-\cos^2{x}=0$ 
Does anyone know why these answers are wrong?
  $$4\sin^2{x}\cos^2{x}-\cos^2{x}=0$$

$(4\sin^2x)(\cos^2x)=\cos^2x$
$4\sin^2x=1$
$\sin x=1/2$
$x=30° , 150°$
Thank you

$(4\sin^2x)(\cos^2x)=\cos^2x$ implies $\cos x=0$ or $4\sin^2x=1$. For $0\le x<360^\circ$, the former is true for $x=90^\circ,270^\circ$ while the latter is true when $\sin x=\pm1/2$, which in turn is true of $30^\circ,150^\circ,210^\circ,330^\circ$.
