数列

\( a_1 = a,\ \ a_2 = b,\ \ p a_{n + 2} + q a_{n + 1} + r a_n = 0 \quad (pqr \neq 0) \quad \) で定められる数列 \( \{ a_n \} \) の一...

等差数列 \( a_{n + 1} = a_n + d \quad \) (公差 \(d\) ) \( \qquad \qquad \qquad \qquad \to \qquad a_n = a_1 + (n\ -\ 1)d \) ...

\( \displaystyle \sum_{k=1}^n k = \dfrac{1}{2}n(n + 1) \) \( \qquad \begin{eqnarray} \displaystyle \sum_{k=1}^n k &...