等差数列前n项和S=((a_1+a_n)n)/2=na_1+(n(n-1))/2d是高考中的重点,是数列部分最重要公式之一,近几年有多元发展的趋势,内容主要涉及对前n项和公式的深刻理解与灵活运用。下面谈谈如何巧用等差数列前n项和公式,供大家在学习时参考。1.直接用公式直接由公式S_n=((a_1+a_n)n)/2=(a_m+a_(n+m+1))/2=na_1+(n(n-1))/2d解题。例1若{a_n}是等差数列,首项a_1>0,a_(2003)+a_(2004)>0, The first n items of arithmetic progression and S = ((a_1 + a_n) n) / 2 = na_1 + (n (n-1)) / 2d are the key points of the college entrance examination and are one of the most important formulas in the sequence. The trend of pluralistic development mainly involves the deep understanding and flexible application of the first n terms and formulas. Here to talk about how to use the arithmetic mean difference before the n and formula for everyone to learn reference. 1. Directly solve the problem directly with the formula S_n = ((a_1 + a_n) n) / 2 = (a_m + a_ (n + m + 1)) / 2 = na_1 + (n (n-1)) / 2d. Example 1 If {a_n} is an arithmetic progression, the first item a_1> 0, a_ (2003) + a_ (2004)> 0,