均值定理
f(x) = (x^2-3x+1)/x= x-3 + (1/x)f'(x) = 1 - 1/x^2f'(x)=01 - 1/x^2=0x^2-1=0x=1f''(x) = 2/x^3f''(1) = 2 >0 (min)f(x) = (x^2-3x+1)/x最小值 f(x)=f(1)=(1-3+1)/1 = -1
拆项后用双勾函数的单调性即可。
