函数f(x)=x³-x²/2-2x+5
f'(x)=3x²-x-2=(x-1)(3x+2)
令f'(x)=0得x1=-2/3,x2=1
列表:
x -1 (-1,-2/3) -2/3 (-2/3,1) 1 (1,2) 2
f'(x) + 0 - 0 +
f(x) 11/2 增 157/27 减 7/2 增 7
f(x)max=7,f(x)min=7/2
∵对任意x∈[-1,2],都有f(x)>m,
∴f(x)min>m
∴m<7/2