Identity :-
<em>( a + b )² = a² + b² + 2ab </em>
Given :-
... 9m² + 30mn + 25n²
<em>Re-writing this :- </em>
... ( 3m )² + ( 2 ) ( 3m ) ( 5n ) + ( 5n )²
<em>We could write this as :- </em>
( 3m + 5n )²
<u><em>Hence, the answer is ( 3m + 5n )²</em></u>