Find the value of x^3 + y^3 + 12xy – 64, when x +y = 4
Since x + y = 4 ---> y = 4 - x
x3 + y3 + 12xy - 64 ---> x3 + (4 - x)3 + 12x(4 - x) - 64
(multiplying out) ---> x3 + [ 64 - 48x + 12x2 - x3 ] + [ 48x - 12x2 ] - 64
(rearranging) ---> x3 - x3 + 64 - 64 - 48x + 48x + 12x2 - 12x2
= 0