2. (a-b)²=(a-b)(a-b)=a²-ab-ab+b²=a²-2ab+b²

3. (a+b)³=(a+b)²(a+b)=(a²+2ab+b²)(a+b)=a³+a²b+2a²b+2ab²+ab²+b³=a³+3a²b+3ab²+b³

4. (a-b)³=(a-b)²(a-b)=(a²-2ab+b²)(a-b)=a³-a²b-2a²b+2ab²+ab²-b³=a³-3a²b+3ab²-b³

5. (a+b)(a-b)=a²-ab+ab-b²=a²-b²

6. (a+b)(a²-ab+b²)=a³-a²b+ab²+a²b-ab²+b³=a³+b³