Prove that $\sin^4(x)\cos^2(x) + \sin^2(x)\cos^4(x) - \sin^2(x)\cos^2(x)=0.$ Using the following expression:
$$\sin^4(x)\cos^2(x) + \sin^2(x)\cos^4(x) - \sin^2(x)\cos^2(x).$$
The above expression is supposed to evaluate to zero, but how?

\begin{align}
\sin^4 x \cos^2 x + \sin^2 x\cos^4 x - \sin^2 x \cos^2 x&=\sin^2 x \cos^2 x\ (\sin^2 x + \cos^2 x - 1)\\
&=\sin^2 x \cos^2 x\ (1-1)\\
&=\large\color{blue}0.
\end{align}
