math
posted by siyad .
find the value of x^3+y^312xy+64 when x+y= 4

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^312xy +64=A
(x+y)(x^2xy+y^2) 12xy +64=A
now divide through by 4
x^2xy+y^2+3xy+64=A/4
x^2+2xy+y^2 =A/464
(x+y)^2=A/464
16=A/464
A=320 which answers the question. 
Better check the ± signs