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2008年高考四川卷理科第16题是:设等差数列{an}的前n项和为Sn,若S4≥10,S5≤15,则a4的最大值为.这是一道设计独特,能力立意高,在知识网络交汇处命制的好题.下面给出它的两种解法及其解题启示.解法1运用整体思想和待定系数法求解.设等差数列{an}的公差为d,令a4=k1S4+k2S5,则有a1
The 16th issue of the Sichuan College of Science in the 2008 National College Entrance Examination Examination was: Let the first n items and the Sn of the {an} series be Sn. If S4≥10 and S5≤15, then the maximum value of the a4 value is. This is a unique design and the ability to develop High, the good question at the intersection of the knowledge network. Here are two solutions to it and their implications. The solution 1 is solved using the overall idea and the undetermined coefficient method. Let the tolerance series {an} have a tolerance of d, Let a4=k1S4+k2S5, then there is a1