Ans: (a) $(m+6n)^2$ (b) $(m+6n+5k)(m+6n-5k)$
-
$\begin{array}{cl}
& m^2+12mn+36n^2 \\
= & (m+6n)^2
\end{array}$ -
$\begin{array}{cl}
& m^2+12mn+36n^2-25k^2 \\
= & (m+6n)^2 – (5k)^2 \\
= & (m+6n+5k)(m+6n-5k)
\end{array}$
