0,求证：g(x)在[m,+无穷）上单调递

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设x2>x1>=m>0g(x2)-g(x1)=f(x2)/x2-f(x1)/x1
={[2x2^2+(x2-m)^2]/x2}-{[2x1^2+(x1-m)^2]/x1}
=(3x2-2m+m^2/x2)-(3x1-2m+m^2/x1)
=3(x2-x1)+(m^2/x2-m^2/x1)
=(x2-x1)[(3x1*x2-m^2)/(x1*x2))>0故g(x)在[m,+无穷）上单调递