Ans: (a) $(r+5)^2$ (b) $(r+s+5)(r-s+5)$
-
$\begin{array}{cl}
& r^2+10r+25 \\
= & r^2 + 2 (r) (5) + 5^2 \\
= & (r+5)^2
\end{array}$ -
$\begin{array}{cl}
& r^2+10r+25-s^2 \\
= & (r+5)^2 -s^2 \\
= & [ (r+5)+s)] [(r+5)-s] \\
= & (r+s+5)(r-s+5)
\end{array}$
