Assertion (A) and Reason (R)
(A) Both A and $\mathrm{R}$ are true and $\mathrm{R}$ is the correct explanation of $\mathrm{A}$.
(B) Both $\mathrm{A}$ and $\mathrm{R}$ are true but $\mathrm{R}$ is not the correct explanation of $\mathbf{A}$.
(C) $\mathrm{A}$ is true, $\mathrm{R}$ is false.
(D) $\mathrm{A}$ is false, $\mathrm{R}$ is true.
Assertion $(\mathrm{A}):$ The least value of the function $f(x)=-x^{2}$ $+4 x+1+\sin ^{-1}\left(\frac{x}{2}\right)$ on the interval $[-1,1]$ is $-4-\frac{\pi}{6}$
Reason $(\mathrm{R}):$ The least value of $\mathrm{f}(\mathrm{x})$ in $[-1,1]=\min (\mathrm{f}(-1)$
$f(1)\}=\min \left\{-4-4 \frac{\pi}{6}, 4+\frac{\pi}{6}\right\}=-4-\frac{\pi}{6}$