Câu hỏi
Hàm số \(y = f\left( x \right)\) đồng biến trên khoảng \(\left( {a;\,b} \right)\) nếu:
A
\(\forall {x_1},{x_2} \in \left( {a;\,\,b} \right),\,\,{x_1} < {x_2} \Rightarrow f\left( {{x_1}} \right) < f\left( {{x_2}} \right)\);
B
\(\forall {x_1},{x_2} \in \left( {a;\,\,b} \right),\,\,{x_1} = {x_2} \Rightarrow f\left( {{x_1}} \right) < f\left( {{x_2}} \right)\);
C
\(\forall {x_1},{x_2} \in \left( {a;\,\,b} \right),\,\,{x_1} < {x_2} \Rightarrow f\left( {{x_1}} \right) > f\left( {{x_2}} \right)\);
D
\(f\left( a \right) < f\left( b \right)\).