定积分，极小值
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∫(0->x-3) f(t) dt = x^3-x^2 +x
两边取导数
f(x-3) = 3x^2-2x
= 3(x-3)^2 +16x -27
= 3(x-3)^2 +16(x-3) +21
f(x) = 3x^2+16x+21
f'(x) = 6x+16
f''(x) =6 >0 (min)
f'(x) =0
6x+16=0
x=-8/3
min f(x) = f(-8/3) = 3(-8/3)^2+16(-8/3)+21 = 64/3 - 128/3+21 = -1/3
两边取导数
f(x-3) = 3x^2-2x
= 3(x-3)^2 +16x -27
= 3(x-3)^2 +16(x-3) +21
f(x) = 3x^2+16x+21
f'(x) = 6x+16
f''(x) =6 >0 (min)
f'(x) =0
6x+16=0
x=-8/3
min f(x) = f(-8/3) = 3(-8/3)^2+16(-8/3)+21 = 64/3 - 128/3+21 = -1/3
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