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.](/uploads/image/z/8859171-3-1.jpg?t=27.%E5%B7%B2%E7%9F%A5x%3D1.25%2Cy%3D-0.64%E6%97%B6%2C%E6%B1%82%5B%28x%2By%293-%28x3%2By3%29%5D%C3%B7%28x%2By%29%E7%9A%84%E5%80%BC.)
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)^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
27.已知x=1.25,y=-0.64时,求[(x+y)3-(x3+y3)]÷(x+y)的值.
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