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math

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find the value of x^3+y^3-12xy+64 when x+y= -4

  • math - ,

    Nothing is more fun that cubic equations, in school, most are trick questions, such as this. In real life, they are challenging.

    x^3+y^3-12xy +64=A
    (x+y)(x^2-xy+y^2) -12xy +64=A
    now divide through by -4
    x^2-xy+y^2+3xy+64=A/4
    x^2+2xy+y^2 =A/4-64
    (x+y)^2=A/4-64
    16=A/4-64
    A=320 which answers the question.

  • math - ,

    Better check the ± signs

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