令x1>x2>=1f(x1)-f(x2)=√(x1-1)-√(x2-1)=[√(x1-1)-√(x2-1)][√(x1-1)+√(x2-1)]/[√(x1-1)+√(x2-1)]=(x1-1-x2+1)/[√(x1-1)+√(x2-1)]=(x1-x2)/[√(x1-1)+√(x2-1)]因为根号内大于0,所以分母>0,又x1>x2所以f(x1...