解设x1,x2属于[1,2],且x1＜x2则f(x1)-f(x2)=x1^2+a/x1-(x2^2+a/x2)=x1^2-x2^2+a(x2-x1)/x1x2=(x1-x2)(x1+x2)+a(x2-x1)/x1x2=(x1-x2)(x1+x2-a/x1x2)由函数f（x）在[1,2]上单调递增且x1-x2＜0故(x1+x2-a/x1x2)＞0恒成...
已知函数f（x）=x2+（a/x） (a属于R)
解设x1,x2属于[1,2],且x1＜x2则f(x1)-f(x2)=x1^2+a/x1-(x2^2+a/x2)=x1^2-x2^2+a(x2-x1)/x1x2=(x1-x2)(x1+x2)+a(x2-x1)/x1x2=(x1-x2)(x1+x2-a/x1x2)由函数f（x）在[1,2]上单调递增且x1-x2＜0故(x1+x2-a/x1x2)＞0恒成...