giải nhanh lên mn

$\displaystyle  \begin{array}{{>{\displaystyle}l}}
Bài\ 8:\ \\
1/\ a^{2} +2ab+b^{2}\\
=a^{2} +ab+ab+b^{2}\\
=a( a+b) +b( a+b)\\
=( a+b)( a+b)\\
=( a+b)^{2} \ ( đpcm)\\
2/\ a^{2} -2ab+b^{2}\\
=a^{2} -ab-ab+b^{2}\\
=a( a-b) -b( a-b)\\
=( a-b)( a-b)\\
=( a-b)^{2} \ ( đpcm)\\
3/\ ( a-b)( a+b)\\
=a^{2} +ab-ab-b^{2}\\
=a^{2} -b^{2} \ ( đpcm)\\
4/\ ( a+b)^{3}\\
=( a+b)( a+b)^{2}\\
=( a+b)\left( a^{2} +2ab+b^{2}\right)\\
=a^{3} +2a^{2} b+ab^{2} +a^{2} b +2ab^{2} +b^{3}\\
=a^{3} +3a^{2} b+3ab^{2} +b^{3} \ ( đpcm)
\end{array}$