If $\phi(x)=\int\limits_{1 / x}^{\sqrt{x}} \sin \left(t^2\right) d t$, then $\phi '(1)$ is equal to
Answer & explanation
Correct answer: option 3
By Leibnitz's rule, we have
$\phi'(x) =\frac{1}{2 \sqrt{x}} \sin x-\left(-\frac{1}{x^2}\right) \sin \frac{1}{x^2}$
$\phi'(1)=\frac{1}{2} \sin 1+\sin 1=\frac{3}{2} \sin 1$