factorization by using identities

(5g-6h)² - 16(4g-3h)²
= (5g-6h)² - [4(4g-3h)]²
= (5g-6h)² - (16g - 12h)²
= ( 5g - 6h + 16g - 12h )( 5g - 6h - 16g + 12h )
= ( 21g - 18h )( -11g + 6h )
= 3( 7g - 6h )( -11g + 6h ) //

2007-02-25 14:31:36 補充：
記條數所需的 identitie and formula: a² - b² = ( a+b )( a-b )a²( b+c )² = [a(b + c)]²

(5g-6h)^2-16(4g-3h)^2
=25g^2-60gh+36h^2-256g^2+384gh-144h^2
=-231g^2 +324gh-108h^2
=-(21g-18h)(11g-6h)