一般地 ,我们不妨称函数　 f(x) =∑ni=1(x - ti) 2为平方和函数 .显然 ,平方和函数具有非负性 .对于条件式为 ∑ni=1xi =a,或∑ni=1x2i= b,待求 (证 )式为 ∑ni=1x2i ≥ c或 d≤ ∑ni=1xi ≤e型的不等式 ,构造平方函数 ,利用其非负性 ,可使问题简捷获解 (证 ) .例 1　 (第 7届 In general, we may call the function f(x) = ∑ni=1(x - ti) 2 as a sum of squares functions. Obviously, the sum of squares functions has a non-negativity. For the conditional formula ∑ni=1xi =a, or Ni=1x2i=b, the formula for 待ni=1x2i ≥ c or d≤ ∑ni=1xi ≤e is an inequality that constructs a square function. Using its non-negativity, the problem can be solved simply ( ). Example 1 (7th Session