故?k,k???242??4??2??4??2??k??或或???,k,k??,2k,k??2,?????????????333??3??3??3??3?2?k??2?242??4???3或?或k?2，?k?或k?或k?2，k????,??????2,???.
333??3???k?4?3?21.解：（1）由已知，x3?ax2?bx?c?(x?x1)(x?x2)(x?x3),比较两边系数，得
x1?x2?x3??a,x,bx. c1x2?x2x3?x3x1??1x2x3?? (2)由已知f'(x)?3x2?2ax?b?0有两个不等的实根?,?因为?1???0???1,由实根分布，则
?3?2a?b?0? 由a?Z,b?Z，b?2则a?0,b?1.所以f'(x)?3x2?1 ??b?0?3?2a?b?0? 则???3333处取得极大值x?取得极小值， ,??,且f(x)在x??3333?3?f(?)?02323?3故f(x)?0要有三个不等根，则必须? 解得?. ?c?99?f(3)?0
?3?