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教材中给出的等差数列前n项和公式为:Sn=n(a1+an)/2=na1+n(n-1)/2d.在具体的解题过程中,如果我们能适时地应用公式的变化形式,则往往能减少运
The first n terms and the formulas given in the textbook are: Sn = n (a1 + an) / 2 = na1 + n (n-1) / 2d In the process of solving the problem, if we can Changes in the application of the formula, you can often reduce the transport