Question

chứng minh 

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

Answer 1

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

Answer 2

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

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

\(=a^3-b^3=VT\)

P/s: chúc bạn học tốt