2011-I-03

20-06-2023 app.cch 尚無留言

答案：(a)

(9 m + n) (9 m - n)

(b)

(9 m - n) (9 m + n + 2)

$\begin{array}{cl} 81 m^{2} - n^{2} \\ = & (9 m - n) (9 m + n) \end{array}$
$\begin{array}{cl} 81 m^{2} - n^{2} + 18 m - 2 n \\ = & (9 m - n) (9 m + n) + 2 (9 m - n) \\ = & (9 m - n) (9 m + n + 2) \end{array}$