设二次函数\(f\left( x \right)=a{{x}^{2}}+bx+c\)的导函数为\({f}{{{"}}}\left( x \right)\),则对\(\forall x\in R\),不等式\(f\left( x \right)\geqslant {f}{{{"}}}\left( x \right)\)恒成立,则\(\dfrac{{{b}^{2}}}{{{a}^{2}}+2{{c}^{2}}}\)的最大值为
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