若2≤x10f(x1)-f(x2)=(x1^2+4/x1)-(x2^2+4/x2）=（x1^2-x2^2)+(4/x1-4/x2)=（x1^2-x2^2)+((x2-x1)/(x1x2)=(x1-x2)[x1x2)(x1+x2)-4]/(x1x2)∵x1x2>4,x1x2-4>0所以x1x2)(x1+x2)-4＞0∴(x1-x2)[x1x2-4]/(x1x2)...那个是x^2不是X你代值带错了吧