A scalar valued function is defined as $f(X)=X^TAX+b^TX+c,$ where A is a symmetric positive definite matrix with dimension $n\times n$; b and X are vectors of dimension $n\times 1$. The minimum value of f(x) will occur when X equals
- $(A^TA)^{-1}b$
- $-(A^TA)^{-1}b$
- $-(\frac{A^{-1}b}{2})$
- $\frac{A^{-1}b}{2}$