等差数列的求和公式
summation formula for an arithmetic sequence The sum of the first $n$ terms of an arithmetic sequence is $S_n = \frac{n(a_1 + a_n)}{2}$ or $S_n = \frac{n[2a_1 +
CSCA 数学 考试术语
summation formula for an arithmetic sequence The sum of the first $n$ terms of an arithmetic sequence is $S_n = \frac{n(a_1 + a_n)}{2}$ or $S_n = \frac{n[2a_1 +
CSCA 数学 考试术语