3.
若\(f\left( x \right)\)是定义在\(\left( -\infty ,+\infty \right)\)上的偶函数,\(\forall {{x}_{1}},{{x}_{2}}\in \left[ 0,+\infty \right)\left( {{x}_{1}}\ne {{x}_{2}} \right)\),有\(\dfrac{f\left( {{x}_{2}} \right)-f\left( {{x}_{1}} \right)}{{{x}_{2}}-{{x}_{1}}} < 0\),则 \((\) \()\)