有些条件表面看来无法利用 ,若能揭示条件的实质 ,则可迅速得到问题的解答 .一、配方例 1　若ａ2 ｂ2 +ａ2 +ｂ2 + 1 -4ａｂ =0 ,则ａ+ｂ的值是 (　　 )(Ａ) 2或 -2　　　　 (Ｂ) 2或 -2或 0(Ｃ) 2 (Ｄ) -2解　由条件得 :(ａｂ-1 ) 2 + (ａ-ｂ) 2 =0 ,故可得ａｂ-1 =0和ａ-ｂ=0 Some conditions appear to be unusable on the surface. If we can reveal the essence of the conditions, we can quickly get the answers to the questions. Formula Example 1 If a2 b2 +a2 +b2 + 1 -4ab =0, the value of a+b is ( ) (A) 2 or -2 (B) 2 or -2 or 0 (C) 2 (D) -2 Solution derived from the condition: (ab-1) 2 + (a-b) 2 =0, so it is available Ab-1 =0 and a-b=0