Question 30050
(3x^3 + 2x^2 +8x) + (x^3 - 5x^2 + 7)
=(3x^3 + x^3)+ (2x^2  - 5x^2)+8x + 7  (grouping like terms which is nothing but repeated additive commutativity and associativity)
=4x^3-3x^2+8x+7