Thinking Mathematically (6th Edition)

Published by Pearson
ISBN 10: 0321867327
ISBN 13: 978-0-32186-732-2

Chapter 7 - Algebra: Graphs, Functions, and Linear Systems - 7.3 Systems of Linear Equations in Two Variables - Exercise Set 7.3 - Page 445: 48

Answer

The solution set is\[\left\{ \left( \frac{1}{2a},\frac{1}{b} \right),a\ne 0,b\ne 0 \right\}\].

Work Step by Step

Multiply \[5\]on both sides to the equation \[4ax+by=3\]to get: \[20ax+5by=15\]. Subtract the second given equation to the above obtained equation from both RHS and LHS as follows: \[\underline{\begin{align} & 20ax+5by=15 \\ & -6ax-5by=-8 \end{align}}\] \[\begin{align} & 14ax\ \ \ \ \ \ \ \ \ \ =7 \\ & x=\frac{1}{2a},\ \ \ \ \ \ a\ne 0 \end{align}\] Put \[x=\frac{1}{2a}\]in\[4ax+by=3\] to get: \[\begin{align} & 4a\left( \frac{1}{2a} \right)+by=3 \\ & 2+by=3 \\ & by=1 \\ & y=\frac{1}{b},\ \ \ \ \ b\ne 0 \end{align}\] To verify put\[y=\frac{1}{b}\]and \[x=\frac{1}{2a}\] in\[6ax+5by=8\]as follows: \[\begin{align} & 6a\left( \frac{1}{2a} \right)+5b\left( \frac{1}{b} \right)=8 \\ & 3+5=8 \\ & 8=8 \end{align}\] RHS\[=\]LHS Hence verified. Hence, the solution set is\[\left\{ \left( \frac{1}{2a},\frac{1}{b} \right),a\ne 0,b\ne 0 \right\}\].
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