作业帮27.已知x=1.25,y=-0.64时,求[(x+y)3-(x3+y3)]÷(x+y)的值.
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27.已知x=1.25,y=-0.64时,求[(x+y)3-(x3+y3)]÷(x+y)的值.
27.已知x=1.25,y=-0.64时,求[(x+y)3-(x3+y3)]÷(x+y)的值.
27.已知x=1.25,y=-0.64时,求[(x+y)3-(x3+y3)]÷(x+y)的值.
27.已知x=1.25,y=-0.64时,求[(x+y)3-(x3+y3)]÷(x+y)的值.
[(x+y)^33-(x^3+y^3)]÷(x+y)
解,得：
==(x+y)^3*1/(x+y)-(x+y)(x^2-xy+y^2)*1/(x+y)
==(x+y)^2-(x^2-xy+y^2)
==x^2+2xy+y^2-x^2+xy-y^2
==3xy
所以得：
3xy
==3*1.25*(-0.64)
==-2.4
(x+y)^3=x^3+3x^2y+3xY^2+3y^3
(x+y)^3-(x3+y3)=3x^2y+3xY^2=3xy(y+x)
[(x+y)3-(x3+y3)]÷(x+y)=3xy=-3*5/4*64/100
=-12/5
[(x+y)³-(x³+y³)]÷(x+y)
=[(x+y)³-(x+y)(x²-xy+y²)]÷(x+y)
=(x+y)²-(x²-xy+y²)
=x²+2xy+y²-x²+xy-y²
=3xy
=3×1.25×(-0.64)<...
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[(x+y)³-(x³+y³)]÷(x+y)
=[(x+y)³-(x+y)(x²-xy+y²)]÷(x+y)
=(x+y)²-(x²-xy+y²)
=x²+2xy+y²-x²+xy-y²
=3xy
=3×1.25×(-0.64)
=-2.4
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