Công thức nào sau đây là đúng để tính độ lệch chuẩn khi biết số trung bình \(\overline{x}\)?
\(s_X^2=\dfrac{1}{n^2}.\left[n_1\left(x_1-\overline{x}\right)^2+n_2\left(x_2-\overline{x}\right)^2+...+n_k\left(x_k-\overline{x}\right)^2\right]\).\(s_X=\dfrac{1}{n^2}.\left[n_1\left(x_1-\overline{x}\right)^2+n_2\left(x_2-\overline{x}\right)^2+...+n_k\left(x_k-\overline{x}\right)^2\right]\).\(s_X=\sqrt{\dfrac{1}{n}.\left[n_1\left(x_1-\overline{x}\right)^2+n_2\left(x_2-\overline{x}\right)^2+...+n_k\left(x_k-\overline{x}\right)^2\right]}\).\(s_X^2=\dfrac{1}{n}.\sqrt{n_1\left(x_1-\overline{x}\right)^2+n_2\left(x_2-\overline{x}\right)^2+...+n_k\left(x_k-\overline{x}\right)^2}\).