f(x)=1/3x^3-mx^2-3m^2x+1f'(x)=x^2-2mx-3m^2=(x-3m)(x+m)因为f(x)在区间(1,2)内是增函数所以3m<=1且-m<=1，或者3m>=2且-m>=2得m范围是[-1,1/3]
