x→0limx3f(x)
Using L Hopital Rule. x→0lim3x2f′(x)=x→0lim3x2x+sin(1−ex) (Again L Hopital) Using L.H. Rule $\begin{aligned}
& =\lim _{x \rightarrow 0} \frac{-\left[\sin \left(1-e^x\right)\left(-e^x\right) \cdot e^x+\cos \left(1-e^x\right) \cdot e^x\right]}{6} \
& =-\frac{1}{6}
\end{aligned}$