Simplify: $\sin^4x + \sin^2x \cdot \cos^2x$
The textbook states the answer as $\sin^2x$ and I understand the reasoning: Take a factor of $\sin^2x$ out and you are left with $\sin^2x \cdot 1$
However I can't work out why my method is wrong (it produces the answer of 1):
Divide everything by $\sin^2x$
$(\sin^4x / \sin^2x)+ (\sin^2x \cdot \cos^2x )/ \sin^2x$
Which cancels down to:
$\sin^2x + \cos^2x$
Which equals $1$.
I managed to get both results when using WolframAlpha to check my working! What am I misunderstanding?