Question

if a + b = -1, then find the value of a^3 + b^3 + 3ab

Answer 1

-1=a^3+b^3+3ab(-1)
=6ab-1

Answer 2

a^3+b^3+3ab= (a+b)(a^2-ab+b^2)+3ab
=-1{(a+b)^2-2ab-ab}+3ab
=-1 {(-1)^2-3ab}+3ab
=-1 (1-3ab)+3ab
=-1+3ab+3ab
=-1+6ab