Ans: (a) $(2m+5n)(2m-5n)$ (b) $(2m-5n)(2m+5n+3)$
-
$\begin{array}{cl}
& 4m^2-25n^2 \\
= & (2m)^2 – (5n)^2 \\
= & (2m+5n)(2m-5n)
\end{array}$ -
$\begin{array}{cl}
& 4m^2-25n^2 + 6m-15n \\
= & (2m+5n)(2m-5n) +3(2m-5n) \\
= & (2m-5n)(2m+5n+3)
\end{array}$
