Solution
= Solution
Differentiating the ball volume with respect to $R$ gives
$$
\boxed{A_{n-1}(R)=\frac{2\pi^{n/2}R^{n-1}}{\Gamma(n/2)}=\frac nR V_n(R).}
$$
= Solution
Differentiating the ball volume with respect to $R$ gives
$$
\boxed{A_{n-1}(R)=\frac{2\pi^{n/2}R^{n-1}}{\Gamma(n/2)}=\frac nR V_n(R).}
$$