- Cấp số nhân (có lời giải chi tiết)

A \({u_3} = 12.\)

B \({u_3} =  - 12.\)                     

C \({u_3} =  - 18.\)         

D \({u_3} = 18.\)

A 1; 0,2; 0,04; 0,0008;  …          

B 2; 22; 222; 2222; …

C x; 2x; 3x; 4x; …

D 1; –x²; x⁴; –x⁶; …

A \({u_5} = \frac{{ - 27}}{{16}}\)       

B \({u_5} = \frac{{ - 16}}{{27}}\)       

C \({u_5} = \frac{{16}}{{27}}\)

D \({u_5} = \frac{{27}}{{16}}\)

A \({u_k} = \sqrt {{u_{k + 1}}.{u_{k + 2}}} \)

B \({u_k} = \frac{{{u_{k - 1}} + {u_{k + 1}}}}{2}\)

C \({u_k} = {u_1}.{q^{k - 1}}\)

D \({u_k} = {u_1} + \left( {k - 1} \right)q\)

A \({S_n} = {u_1}\frac{{{q^n} - 1}}{{q - 1}}\)         

B \({S_n} =  - {u_1}\frac{{1 - {q^n}}}{{1 - q}}\)

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

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

A \(q = 3\)

B \(q = 2\)                       

C \(q = 4\)

D \(q = \emptyset \)

A \({u_n} = 2n\)

B \({u_n} = {4.3^n}\)

C \({u_n} = \frac{2}{n}\)          

D \({u_n} = \frac{{{2^n} - 1}}{3}\)

A \(S = 390.\)                  

B \(S = 255.\)                  

C \(S = 256.\)      

D \(S =  - 256.\)

A Thứ 5

B Thứ 6

C Thứ 7

D Không phải là số hạng của cấp số

A \(21;\;63;\;189.\)                    

B \(18;\;54;\;162.\)

C \(15;\;45;\;135.\)

D Tất cả đều sai

A \({S_{10}} = \frac{{59048}}{{12383}}\)

B \({S_{10}} = \frac{{59123148}}{{19683}}\)

C \({S_{10}} = \frac{{1359048}}{{3319683}}\)        

D \({S_{10}} = \frac{{59048}}{{19683}}\)

A \(S = \frac{9}{2}({3^{20}} + 1)\)

B \(S = \frac{9}{2}({3^{20}} - 1)\)

C \(S = \frac{9}{2}({3^{10}} - 1)\)

D \(S = \frac{7}{2}({3^{10}} - 1)\)

A \(x =  \pm 1\)

B \(x =  \pm 2\)   

C \(x =  \pm \sqrt 2 \)      

D \(x =  \pm \sqrt 3 \)

A \((x;y) = \left( {0;0} \right);\left( {\frac{1}{3};\frac{4}{3}} \right);\left( { - \frac{3}{4}; - \frac{3}{{10}}} \right)\)

B \((x;y) = \left( {0;0} \right);\left( {\frac{{10}}{3};\frac{4}{3}} \right);\left( { - \frac{3}{4}; - \frac{3}{{10}}} \right)\)

C \((x;y) = \left( {1;0} \right);\left( {\frac{{11}}{3};\frac{4}{3}} \right);\left( { - \frac{3}{4}; - \frac{3}{{10}}} \right)\)

D \((x;y) = \left( {0;1} \right);\left( {\frac{{10}}{3};\frac{4}{3}} \right);\left( { - \frac{{13}}{4}; - \frac{{13}}{{10}}} \right)\)

A \((x;y) = \left( { - 3; - 1} \right);\left( {1;\;\frac{1}{3}} \right)\)

B \((x;y) = \left( { - 3; - 1} \right);\left( {\frac{1}{3};\frac{1}{3}} \right)\)              

C \((x;y) = \left( {3;1} \right);\left( {\frac{3}{8};\frac{1}{8}} \right)\)

D \((x;y) = \left( { - 3; - 1} \right);\left( {\frac{{12}}{8};\frac{1}{8}} \right)\)

A \(q = 3;{u_n} = \frac{{{3^{n - 1}}}}{{11}}\)          

B \(q = \frac{1}{3};{u_n} = \frac{{81}}{{11}}.\frac{1}{{{3^{n - 1}}}}\)                          

C Cả A, B đúng

D Cả A, B sai    

A \({u_1} = 1;\;{u_1} = 2\)

B \({u_1} = 1;\;{u_1} = 8\)

C \({u_1} = 1;\;{u_1} = 5\)

D \({u_1} = 1;\;{u_1} = 9\)

A \(\left[ \begin{array}{l}m =  - \frac{{10}}{{27}}\\m = 0\end{array} \right.\)          

B \(\left[ \begin{array}{l}m = \frac{{10}}{7}\\m = 0\end{array} \right.\)                   

C \(\left[ \begin{array}{l}m =  - 1\\m = 0\end{array} \right.\)   

D Không có giá trị nào của \(m\)