Question

Rút gọn biểu thức:

( a + b )³ - ( a - b)³ - 2b³

Answer 1

=a^3+b^3+3a^2b+3ab^2-a^3+3a^2b-3ab^2+b^3-2b^3

=6a^2b

Answer 2

\(\left(a+b\right)^3-\left(a-b\right)^3-2b^3\\ =a^3+3a^2b+3ab^2+b^3-\left(a^3-3a^2b+3ab^2-b^3\right)-2b^3\\ =a^3+3a^2b+3ab^2+b^3-a^3+3a^2b-3ab^2+b^3-2b^3\\ =6a^2b\)