Asked by siyad
find the value of x^3+y^3-12xy+64 when x+y= -4
Answers
Answered by
bobpursley
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.
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.
Answered by
Steve
Better check the ± signs
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