Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 9 - Systems and Matrices - 9.3 Determinant Solution of Linear Systems - 9.3 Exercises - Page 886: 73

Answer

\[\left\{ {\left( { - 4,12} \right)} \right\}\]

Work Step by Step

\[\begin{gathered} \left\{ {\begin{array}{*{20}{c}} {\frac{1}{2}x + \frac{1}{3}y = 2} \\ {\frac{3}{2}x - \frac{1}{2}y = - 12} \end{array}} \right. \hfill \\ {\text{Given the system}} \hfill \\ \left\{ {\begin{array}{*{20}{c}} {{a_1}x + {b_1}y = {c_1}} \\ {{a_2}x + {b_2}y = {c_2}} \end{array}} \right. \hfill \\ D = \left| {\begin{array}{*{20}{c}} {{a_1}}&{{b_1}} \\ {{a_2}}&{{b_2}} \end{array}} \right|,\,\,\,{D_x} = \left| {\begin{array}{*{20}{c}} {{c_1}}&{{b_1}} \\ {{c_2}}&{{b_2}} \end{array}} \right|,\,\,{D_y} = \left| {\begin{array}{*{20}{c}} {{a_1}}&{{c_1}} \\ {{a_2}}&{{c_2}} \end{array}} \right| \hfill \\ {\text{First find }}D,{\text{ If }}D \ne 0,\,{\text{ then find }}{D_x}{\text{ and }}{D_y} \hfill \\ D = \left| {\begin{array}{*{20}{c}} {1/2}&{1/3} \\ {3/2}&{ - 1/2} \end{array}} \right| = - \frac{1}{4} - \frac{1}{2} = - \frac{3}{4} \hfill \\ {D_x} = \left| {\begin{array}{*{20}{c}} 2&{1/3} \\ { - 12}&{ - 1/2} \end{array}} \right| = - 1 + 4 = 3 \hfill \\ {D_y} = \left| {\begin{array}{*{20}{c}} {1/2}&2 \\ {3/2}&{ - 12} \end{array}} \right| = - 6 - 3 = - 9 \hfill \\ {\text{Using the Cramer's rule}} \hfill \\ x = \frac{{{D_x}}}{D} = \frac{3}{{ - 3/4}} = - 4,\,\,\,\,\,\,\,\,\,y = \frac{{{D_y}}}{D} = \frac{{ - 9}}{{ - 3/4}} = 12 \hfill \\ {\text{The solution set is}} \hfill \\ \left\{ {\left( { - 4,12} \right)} \right\} \hfill \\ \end{gathered} \]
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