Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 7 - Section 7.4 - Systems of Nonlinear Equations in Two Variables - Exercise Set - Page 851: 46

Answer

The numbers are, $3\ \text{and 2}$, $3\ \text{ and }-2$, $-3\ \text{and 2}$ and $-3\ \text{ and }-2$

Work Step by Step

Let the numbers be $ x $ and $ y $ such that: $\begin{align} & {{x}^{2}}-{{y}^{2}}=5\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \left( \text{I} \right) \\ & 3{{x}^{2}}-2{{y}^{2}}=19\ \ \ \ \ \ \ \ \ \ \ \ \ \ \left( \text{II} \right) \end{align}$ By multiplying equation (I) by $-2$ and adding equation (I) and equation (II): we get, $\begin{align} & -2{{x}^{2}}+2{{y}^{2}}=-10 \\ & \underline{3{{x}^{2}}-2{{y}^{2}}=19} \\ & {{x}^{2}}=9 \\ & x=\pm 3 \\ \end{align}$ Substitute $x=3$ in equation (I): $\begin{align} & {{\left( 3 \right)}^{2}}-{{y}^{2}}=5 \\ & {{y}^{2}}=4 \\ & y=\pm 2 \end{align}$ Substitute $x=-3$ in equation (II): $\begin{align} & {{\left( -3 \right)}^{2}}-{{y}^{2}}=5 \\ & {{y}^{2}}=4 \\ & y=\pm 2 \end{align}$ Thus, the numbers are $3\ \text{and 2}$, $3\ \text{ and }-2$, $-3\ \text{and 2}$ or $-3\ \text{ and }-2$.
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