4A
a) hằng đẳng thức \(A^3+B^3=\left(A+B\right)\left(A^2+AB+B^2\right)\)
b) hằng đẳng thức \(\left(A+B\right)^3=A^3+3A^2B+3AB^2+B^2\)
4A
\(A=\left(a+b+a-b\right)\left[\left(a+b\right)^2+\left(a+b\right)\left(a-b\right)+\left(a-b\right)^2\right]\)
\(A=2a\left(a^2+2ab+b^2+a^2-b^2+a^2+2ab+b^2\right)\)
\(A=2a\left(3a^2+4ab+b^2\right)\)
\(A=6a^3+8a^2b+2ab^2\)