| 等差数列 | 等比数列 | |
|---|---|---|
| 定义 | (a_{n+1} - a_n = d) | (dfrac{a_{n+1}}{a_n}) |
| 通项 | (a_n=a_1+(n-1)d) | (a_n=a_1q^{n-1}) |
| 等差中项:若a，b，c成等差、比数列，则b叫做a与c的等差中项，且 | (b=dfrac{a+c}{2}) | (b^2 =ac) |
| 等和性:若m+n=p+q，则 | (a_m+a_n=a_p+a_q) | (a_m*a_n=a_p*a_q) |
| 前n项和 | (S_n = dfrac{n(a_1+a_n)}{2}) | 当(q eq 1)时，(S_n = dfrac{a_1(1-q^n)}{1-q} = dfrac{a_1-a_nq}{1-q})，当q = 1时，Sn = na1 |
