已知x-y=3,x²+ y²=13,求x³y-8x²y²+xy³的值
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已知x-y=3,x²+ y²=13,求x³y-8x²y²+xy³的值
已知x-y=3,x²+ y²=13,求x³y-8x²y²+xy³的值
已知x-y=3,x²+ y²=13,求x³y-8x²y²+xy³的值
∵X-Y=3,
∴X^2-2XY+Y^2=9,
又X^2+Y^2=13,
∴-2XY=-4,
XY=2
x³y-8x²y²+xy³
=XY(X^2-8XY+Y^2)
=XY[(X^2+Y^2)-8XY]
=2×[13-16]
=-6.
(x-y)²=x²+y²-2xy=3 因为 x²+y²=13 所以 13-2xy=3 所以 xy=5
x³y-8x²y²+xy³=xy(x²-8xy+y²)=5(13-40)=-135
(x-y)² = x² -2xy + y² = 9
因为 x²+ y²=13
所以 xy = 2
x³y-8x²y²+xy³
=xy( x² -8xy + y²)
= xy(x²+ y² -8xy )
= 2*(13 -...
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(x-y)² = x² -2xy + y² = 9
因为 x²+ y²=13
所以 xy = 2
x³y-8x²y²+xy³
=xy( x² -8xy + y²)
= xy(x²+ y² -8xy )
= 2*(13 - 8*2)
= - 6
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