【正文】
4 . 平方差公式有八種變化形式: (1) 位置變化: ( b + a )( - b + a ) = a 2 - b 2 . (2) 符號(hào)變化: ( - a - b )( a - b ) = b 2 - a 2 . (3) 系數(shù)變 化: ??? ???12 a + 2 b ??? ???12 a - 2 b = ??? ???12 a 2 - (2 b ) 2 . (4) 指數(shù)變化: ( a 2 + b 2 )( a 2 - b 2 ) = ( a 2 ) 2 - ( b 2 ) 2 . (5) 增項(xiàng)變化: ( a + b - c ) ( a - b + c ) = a 2 - ( b - c ) 2 . (6) 增因式變化: ( a + b )( a - b )( - a - b )( - a + b ) = ( a 2 - b 2 )( a 2 - b 2 ) = ( a 2 - b 2 ) 2 . (7) 連用公式變化: ( a - b )( a + b )( a 2 + b 2 )( a 4 + b 4 ) = a 8 - b 8 . (8) 逆用公式變化: ( a - b + c - d ) 2 - ( a + b - c + d ) 2 = 2 a ( - 2 b + 2 c - 2 d ) = 4 a ( - b + c - d ) . 【例