Posted by **siyad** on Monday, July 9, 2012 at 7:56am.

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

- math -
**bobpursley**, Monday, July 9, 2012 at 9:53am
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 -
**Steve**, Monday, July 9, 2012 at 10:44am
Better check the ± signs

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