Assertion (A) : If  $y\left(x\right)=\underset{\frac{{\pi }^2}{16}}{\overset{x^2}{\int }}\frac{\cos x.\cos \sqrt{\theta }}{1+{\sin }^2\sqrt{\theta }}d\theta ,$  then at  $x=\pi ,\frac{dy}{dx}=\pi$
Reason (R) :  $\frac{d}{dx}\underset{a\left(x\right)}{\overset{b\left(x\right)}{\int }}f\left(t\right)dt=f\left(b\right(x\left)\right)\frac{db}{dx}-f\left(a\right(x\left)\right)\frac{da}{dx}$

Both A and R are individually true but R is not the correct explanation of A

A is false but R is true

A is true but R is false

Both A and R are individually true and R is the correct explanation of A