Differentiate $y = x^2 e^x$ with respect to $x$.

Apply the product rule $\dfrac{d}{dx}(uv) = u'v + uv'$ with $u = x^2$ and $v = e^x$: $2x e^x + x^2 e^x = x e^x (2 + x)$. Differentiating only the $x^2$ factor gives $2x e^x$, which is incomplete.