How to :-
Factorise using identities.
[49 (a-b)^2]-[25 (a+b)^2]
[Note that ^ means exponent ]
49(a-b)2 -25 (a+b)2 = {7(a-b)}2 - {5(a+b)}2
But we know that (a+b) * ( a-b) = (a2 - b2)
Therefore {7(a-b)}2- {5(a+b)}2= {7(a-b)}+{5(a+b)} * {7(a-b)}- {5(a+b)}
= (7a - 7b + 5a +5b) * ( 7a - 7b - 5a -5b ) = (12 a - 2b) * ( 2a - 12b) = 2 * ( 6a-b) * 2 ( a-6b)
= 4 * ( 6a-b) (a-6b) (Answer)