Cho \(f\left( x \right) = a{x^2} + bx + c\,{\rm{ }...

Câu hỏi: Cho \(f\left( x \right) = a{x^2} + bx + c\,{\rm{ }}\left( {a \ne 0} \right).\) Điều kiện để \(f\left( x \right) > 0\,,{\rm{ }}\forall x \in R\) là

A. \(\left\{ \begin{array}{l} a > 0\\ \Delta \le 0 \end{array} \right..\)

B. \(\left\{ \begin{array}{l} a > 0\\ \Delta \ge 0 \end{array} \right..\)

C. \(\left\{ \begin{array}{l} a > 0\\ \Delta < 0 \end{array} \right..\)

D. \(\left\{ \begin{array}{l} a < 0\\ \Delta > 0 \end{array} \right..\)