Let `f(x)=Sigma_(i=1)^(n) (x-x_i)^2`, where `x_i` are real coefficients , then which of the following is/are incorrect ?

A. f(x) attains its least value at `x=1/n underset(i=1)overset(n)Sigmax_i`

B. f(x) attains its least value of `x=(x_1+2x_2+3x_3+.....+nx_n)/n`

C. f(x) attains its least value of `x=n underset(i=1)overset(n)Sigmax_i`

D. f(x) attains its least value at `x=underset(i=1)overset(n)Sigmax_i`