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

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

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

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

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