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解: 7 ( x – 3 ) – x ( 3 – x ) = = ( x – 3 ) ( 7 + x ). 想一想 當 n為偶數(shù): ( a – b )n = (b – a )n 當 n為奇數(shù): ( a – b )n = – (b – a )n ( a – b )1 = – (b – a )1 ( a – b )2 = (b – a )2 ( a – b )3 = – (b – a )3 ( a – b )4 = (b – a )4 …… …… 從中你能發(fā)現(xiàn)什么規(guī)律? 例 3 把 18b ( b – a )2 – 12 ( a – b )3分解因式 . 例 3 把 18b ( b – a )2 – 12 ( a – b )3分解因式 . 18b ( b – a )2 – 12 ( a – b )3 18b ( a – b )2 – 12 ( a – b )3 6( a – b )2 6( a – b )2 ( 3b – 2a + 2b ) 6( a –