VÌ:
\(a-b=3\\ \Rightarrow\left(a-b\right)^2=3^2=9\)
\(\Leftrightarrow a^2-2ab+b^2=9\\ a^2-2\cdot270+b^2=9\\ \Rightarrow a^2+b^2=549\)
Ta có:
\(a^3-b^3=\left(a-b\right)\cdot\left(a^2+ab+b^2\right)=3\cdot\left(549+270\right)=3\cdot819=2457\)
Ta có: \(A=a^3-b^3=\left(a-b\right).\left(a^2+ab+b^2\right)=3.\left(a^2+270+b^2\right)=3a^2+3b^2+810\)
https://i.imgur.com/b8CWBZV.jpg
