a具有两个非负性 :(1 )被开方数非负 ,即 a≥ 0 ;(2 )算术平方根非负 ,即a≥ 0。灵活应用这两个性质可以巧解许多问题。例 1　实数 a满足 |1 992 - a|+a- 1 993=a,那么　 a- 1 992 2的值是(　　 )。(A) 1 991 ;　　 (B) 1 992 ;(C) 1 993;　　 (D) 1 994。解 :由被开方数非负有 a has two non-negativity: (1) the squared number is non-negative, that is a ≥ 0; (2) the square root of the arithmetic is non-negative, ie a≥0. The flexible application of these two properties can solve many problems. Example 1 The real number a satisfies |1 992 − a|+a− 1 993=a, then the value of a- 1 992 2 is ( ). (A) 1 991; (B) 1 992; (C) 1 993; (D) 1 994. Solution : Non-negative