DẠNG 2. CẤP SỐ NHÂN

\({u_{n + 1}} = {u_n} + q\left( {n \in {\mathbb{N}^*}} \right).\)

\({{\rm{u}}_{{\rm{n}} + 1}} = {{\rm{u}}_{\rm{n}}} - {\rm{q}}\left( {{\rm{n}} \in {\mathbb{N}^*}} \right).\)

\({{\rm{u}}_{{\rm{n}} + 1}} = {{\rm{u}}_{\rm{n}}} \cdot {\rm{q}}\left( {{\rm{n}} \in {\mathbb{N}^*}} \right).\)

\({{\rm{u}}_{{\rm{n}} + 1}} = {{\rm{u}}_{\rm{n}}}:{\rm{q}}\left( {{\rm{n}} \in {\mathbb{N}^*}} \right).\)

\({{\rm{u}}_{{\rm{n}} + 1}} = {{\rm{u}}_1} + {\rm{nq}}\left( {{\rm{n}} \in {\mathbb{N}^*}} \right).\)

\({u_{n + 1}} = {u_1} + (n - 1)q\left( {n \in {\mathbb{N}^*}} \right).\)

\({u_{n + 1}} = {u_1} \cdot {q^n}\left( {n \in {\mathbb{N}^*}} \right).\)

\({{\rm{u}}_{{\rm{n}} + 1}} = {{\rm{u}}_1} \cdot {{\rm{q}}^{{\rm{n}} - 1}}\left( {{\rm{n}} \in {\mathbb{N}^*}} \right).\)

\({{\rm{S}}_{\rm{n}}} = \frac{{{{\rm{u}}_1}\left( {1 - {{\rm{q}}^{\rm{n}}}} \right)}}{{{\rm{q}} - 1}}.\)

\({{\rm{S}}_{\rm{n}}} = \frac{{{{\rm{u}}_1}}}{{1 - {\rm{q}}}}.\)

\({S_n} = {u_1}\left( {1 - {q^n}} \right).\)

\({{\rm{S}}_{\rm{n}}} = \frac{{{{\rm{u}}_1}\left( {1 - {{\rm{q}}^{\rm{n}}}} \right)}}{{1 - {\rm{q}}}}.\)

\({S_n} = \frac{{1 - {q^n}}}{{1 - q}}.\)

\({{\rm{S}}_{\rm{n}}} = {{\rm{u}}_1} \cdot \frac{{1 - {{\rm{q}}^{{\rm{n}} - 1}}}}{{1 - {\rm{q}}}}.\)

\({{\rm{S}}_{\rm{n}}} = {{\rm{u}}_1} \cdot \frac{{1 - {{\rm{q}}^{\rm{n}}}}}{{1 - {\rm{q}}}}.\)

\({{\rm{S}}_{\rm{n}}} = \frac{{\left( {{{\rm{u}}_1} + {{\rm{u}}_{\rm{n}}}} \right){{\rm{q}}^{\rm{n}}}}}{2}.\)

10.

9.

11.

12.

\(1;2;4;10; \ldots \)

\(1;2;3;4; \ldots \)

\(18;6;3;1; \ldots \)

\(2;4;8;16; \ldots \)

\(10; - 10;10; - 10; \ldots \)

\(1;2;3;5; \ldots \)

\(1;4;16;64; \ldots \)

72.

81.

96.

100.

\({\rm{q}} = 3.\)

\({\rm{q}} = \frac{1}{3}.\)

\({\rm{q}} = \frac{1}{2}.\)

\({\rm{q}} = 2.\)