Suite arithmétique
\(u_{n+1} - u_n = r\) → variation
\(S_n = \frac{n}{2}(u_1 + u_n)\)

Suite géométrique
\(\frac{u_{n+1}}{u_n} = r\) → variation
\(S_n = u_1 \frac{1-r^n}{1-r}\)

Suite arithmético-géométrique
\(u_{n+1} = a u_n + b\)
\(v_n = u_n - \frac{b}{1-a}\)
\(v_n = v_1 \cdot a^{n-1}\)