\(E=mc^2\)
\[
\begin{split}
F(X)=1 \\
K(x)=\sqrt{x}
\end{split}
\] 
\[
\begin{align}
E(S^2) &=E\left(\frac{1}{n} \sum_{i=1}^n
(X_i-\bar{X})^2\right) \\
& =E\left(\frac{1}{n}\sum_{i=1}^n X_i^2\right) -
E\left(\frac{1}{n}\sum_{i=1}^n 2\bar{X}X_i\right) +
E\left(\frac{1}{n}\sum_{i=1}^n \bar{X}^2\right) \\
& =EX^2 -E(\bar{X}^2) \\
& =DX + (EX)^2 - D\bar{X} - (E\bar{X})^2 \\
& =\frac{n-1}{n}DX
\end{align}
\]