Question

If x+2y=4,xy=2,find x³+8y³

Answer 1

(x+2y)$(x+2y)^3 =x^3+2y^3+3x(2y)(x+2y)\\4^3=x^3+8y^3+6*2*4\\64=x^3+8y^3+48\\64-48=x^3+8y^3\\16=x^3+8y^3$