Factorise:
25(2a−b)2−81b2
we know the algebraic identity
x² - y² = ( x + y )(x - y )
Now ,
25(2a - b )² - 81b²
= [ 5 ( 2a - b )]² - ( 9b)²
= ( 10a - 5b )² - ( 9b )²
= ( 10a - 5b + 9b )(10a -5b - 9b )
= ( 10a + 4b ) ( 10a - 14b )
= [ 2 ( 5a + 2b ) ] [ 2( 5a - 7b )]
= 4(5a + 2b )(5a - 7b )