Giải hệ phương trình tuyến tính \[\left\{ \begin{array}{l}2{x_1} + 7{x_2} + 3{x_3} + {x_4} = 5\\{x_1} + 3{x_2} + 5{x_3} - 2{x_4} = 3\\{x_1} + 5{x_2} - 9{x_3} + 8{x_4} = 1\\5{x_1} + 18{x_2} + 4{x_3} + 5{x_4} = 12\end{array} \right.\]

C. \[{x_1} = 1,{x_2} = 3 - 2{x_3},{x_3} = 4 + 2{x_3}\]

C. \[{x_1} = - 4,{x_2} = - 6 + 3{x_3},{x_4} = 7 - 9{x_3}\]

A. \[\eta \left( {\left( {{x_1},{y_1}} \right),\left( {{x_2},{y_2}} \right)} \right) = 2{x_1}{x_2} + 13{x_1}{y_2} - 5{y_1}{y_2}\]

B. \[\eta \left( {\left( {{x_1},{y_1}} \right),\left( {{x_2},{y_2}} \right)} \right) = 3{x_1}{x_2} + {x_1}{y_2} + 2{x_2}{y_1} + 3{y_1}{y_2}\]

C. \[\eta \left( {\left( {{x_1},{y_1}} \right),\left( {{x_2},{y_2}} \right)} \right) = 2{x_1}{x_2} - 4{x_1}{y_2} + 4{x_2}{y_1} - 2{y_1}{y_2}\]

D. \[\eta \left( {\left( {{x_1},{y_1}} \right),\left( {{x_2},{y_2}} \right)} \right) = {x_1}{y_2} + {x_2}{y_1} - 3{y_1}{y_2}\]

A. 2

B. \[{e^2} - 1\]

C. \[2e + 2\]

D. e

A. \[ln\left| {x - 2} \right| - ln\left| {x - 4} \right| + C\]

B. \[ln\left| {x - 5} \right| - ln\left| {x - 2} \right| + C\]

C. \[\frac{{ln\left| {x - 5} \right|}}{{ln\left| {x - 2} \right|}} + C\]

D. \[ln\left| {\left( {x - 4} \right)\left( {2 - 2} \right)} \right| + C\]

A. \[\frac{{3\pi }}{2}\]

B. \[\frac{\pi }{4}\]

C. 1

D. 0