①已知a-b=2,ab=2,求ab=2,求a³b-2a²b²+ab³的值?
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①已知a-b=2,ab=2,求ab=2,求a³b-2a²b²+ab³的值?
②已知:2x-y=12,x+2y=11,则(2x-y)³-(2x-y)³(x-3y)
②已知:2x-y=12,x+2y=11,则(2x-y)³-(2x-y)³(x-3y)
(1)a-b=2,ab=2
a³b-2a²b²+ab³
=ab(a²-2ab+b²)
=ab(a-b)²
=2×2²
=8
2 2x-y=12.(1)
,x+2y=11.(2)
由(1)得 y=2x-12
把y=2x-12代入(2)得
x+2(2x-12)=11
x+4x-24=11
5x=35
x=7
则y=2x-12=2×7-12=2
所以x=7,y=2
则(2x-y)³-(2x-y)³(x-3y)
=(2x-y)³(1-x+3y)
=12³×(1-7+3×2)
=12³×0
=0
简单解法:由 2x-y=12.(1)
,x+2y=11.(2)
(1)-(2)得
x-3y=1
(2x-y)³-(2x-y)³(x-3y)
=(2x-y)³(1-x+3y)
=(2x-y)³[1-(x-3y)]
=12³×(1-1)
=0
a³b-2a²b²+ab³
=ab(a²-2ab+b²)
=ab(a-b)²
=2×2²
=8
2 2x-y=12.(1)
,x+2y=11.(2)
由(1)得 y=2x-12
把y=2x-12代入(2)得
x+2(2x-12)=11
x+4x-24=11
5x=35
x=7
则y=2x-12=2×7-12=2
所以x=7,y=2
则(2x-y)³-(2x-y)³(x-3y)
=(2x-y)³(1-x+3y)
=12³×(1-7+3×2)
=12³×0
=0
简单解法:由 2x-y=12.(1)
,x+2y=11.(2)
(1)-(2)得
x-3y=1
(2x-y)³-(2x-y)³(x-3y)
=(2x-y)³(1-x+3y)
=(2x-y)³[1-(x-3y)]
=12³×(1-1)
=0
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