Question

a^3+b^3=(a+b)(a^2-ab+b^2)
derivation

Answer 1

a3+b3 = (a+b) (a2-ab+b2) 
and 
a3-b3 = (a-b)(a2+ab+b2) 
Hey its very easy to remember the two. 
Just look and compare both of them. 
When its "+" on the left hand side(i,e a3+b3) then there is "+" in (a+b) and "-" in the middle term of (a2-ab+b2)