(x-4)^2=2x
x^2-8x+16=2x
x^2-10x+16=0
(x-8)(x-2)=0
x=2x=8 w代入y=x-4得
y=-2y=4
y=x-4
x=y+4
y^2=2x
x=y^2/2
当-24)y^2dy
=y^2/2 |(-2->4) +4y|(-2->4) -y^3/6 |(-2->4)
=(16/2-4/2) +4(4-(-2))-1/6(4^3-(-2)^3)
=6+24-12
=18请问这一步S=∫(-2->4) (y+4-y^2/2)dy怎么来的在Y轴上当-2
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