296. $f(x)=x^{3} \sin x$.

296. $f(x)=x^{3} \sin x$. 

The translation is provided while retaining the original format and line breaks. However, since the original text is a mathematical expression, the translation is identical to the source text as it is already in English.
Solution. Applying formulas IV, X and considering that $(\sin x)^{\prime}=$ $=\cos x$, we find

$f^{\prime}(x)=\left(x^{3}\right)^{\prime} \sin x+(\sin x)^{\prime} x^{3}=3 x^{2} \sin x+x^{3} \cos x=x^{2}(3 \sin x+x \cos x)$.