等差数列的求和公式
summation formula for an arithmetic sequence Common formulas are $S_n = \frac{n(a_1 + a_n)}{2}$ or $S_n = \frac{n[2a_1 + (n-1)d]}{2}$.
CSCA 数学 考试术语
summation formula for an arithmetic sequence Common formulas are $S_n = \frac{n(a_1 + a_n)}{2}$ or $S_n = \frac{n[2a_1 + (n-1)d]}{2}$.
CSCA 数学 考试术语