\(\left(a+b\right)^3-\left(a-b\right)^3\)
\(=\left(a+b-a-b\right)\left[\left(a+b\right)^2+\left(a+b\right)\left(a-b\right)+\left(a-b\right)^2\right]\)
\(=0.\left[\left(a+b\right)^2+\left(a+b\right)\left(a-b\right)+\left(a-b\right)^2\right]\)
= 0
( a + b)3 - ( a - b )3
= [ ( a + b) - ( a - b) ][( a + b)2 + ( a + b)( a - b) + ( a - b)2 ]
= ( a + b - a + b)( a2 + 2ab + b2 + a2 - b2 + a2 -2ab + b2)
= 2b( 3a2 + b2)