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Find the determinant in Exercise 19, where \[\left| {\begin{aligned}{*{20}{c}}{\bf{a}}&{\bf{b}}&{\bf{c}}\\{\bf{d}}&{\bf{e}}&{\bf{f}}\\{\bf{g}}&{\bf{h}}&{\bf{i}}\end{aligned}} \right| = {\bf{7}}\].

19. \[\left| {\begin{aligned}{*{20}{c}}{\bf{a}}&{\bf{b}}&{\bf{c}}\\{{\bf{2d}} + {\bf{a}}}&{{\bf{2e}} + {\bf{b}}}&{{\bf{2f}} + {\bf{c}}}\\{\bf{g}}&{\bf{h}}&{\bf{i}}\end{aligned}} \right|\]

Short Answer

Expert verified

Hence, \[\left| {\begin{aligned}{*{20}{c}}a&b&c\\{2d + a}&{2e + b}&{2f + c}\\g&h&i\end{aligned}} \right| = 14\].

Step by step solution

01

Reduce the given determinant

At row 2, add \[ - 1\] time row 1 to row 2 to obtain:

\[\begin{aligned}{c}\left| {\begin{aligned}{*{20}{c}}a&b&c\\{2d + a}&{2e + b}&{2f + c}\\g&h&i\end{aligned}} \right| = \left| {\begin{aligned}{*{20}{c}}a&b&c\\{2d}&{2e}&{2f}\\g&h&i\end{aligned}} \right|\\ = 2\left| {\begin{aligned}{*{20}{c}}a&b&c\\d&e&f\\g&h&i\end{aligned}} \right|\end{aligned}\]

02

Use the given statement

The given statement is \[\left| {\begin{aligned}{*{20}{c}}a&b&c\\d&e&f\\g&h&i\end{aligned}} \right| = 7\].

03

Conclusion

Therefore,

\[\begin{aligned}{c}\left| {\begin{aligned}{*{20}{c}}a&b&c\\{2d + a}&{2e + b}&{2f + c}\\g&h&i\end{aligned}} \right| = 2\left( 7 \right)\\ = 14\end{aligned}\]

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