5a2- b2- 4ab+ 7a - 7b
= 4a2 + a2 - b2 - 4ab + 7a - 7b
= a2 - b2 + 4a2 - 4ab + 7a - 7b
= ( a2 - b2 ) + 4a( a - b ) + 7( a - b )
= ( a - b )( a + b ) + 4a( a - b ) + 7( a - b ) [ a2 - b2 = ( a + b )( a - b ) ]
= ( a - b )[ ( a + b ) + 4a + 7 ]
= ( a - b )[ ( a + b ) + 4a + 7 ]
= ( a - b )[ 5a + b + 7 ]
