College Algebra (10th Edition)

Published by Pearson
ISBN 10: 0321979478
ISBN 13: 978-0-32197-947-6

Chapter 2 - Section 2.1 - The Distance and Midpoint Formulas - 2.1 Assess Your Understanding - Page 155: 50

Answer

$(0,-3-2\sqrt{5}) $ and $ (0,-3+2\sqrt{5})$

Work Step by Step

A point on the $y$ axis has coordinates $P_{1}(0,y).$ Given $P_{2}(4,-3)$, we find $x$ from $ \begin{aligned}&\\ d(P_{1},P_{2})&=\sqrt{(x_{2}-x_{1})^{2}+(y_{2}-y_{1})^{2}}\\ 6&=\sqrt{(4-0)^{2}+(-3-y)^{2}}\\ 6^{2}&=(4-0)^{2}+(-3-y)^{2}\\ 36&=16+9+6y+y^{2}\\ 0&=y^{2}+6y-11 \end{aligned}$ Using the quadratic formula, $y=\displaystyle \frac{-b\pm\sqrt{b^{2}-4ac}}{2a}=$ $=\displaystyle \frac{-6\pm\sqrt{36+44}}{2}=$ $=\displaystyle \frac{-6\pm\sqrt{80}}{2}$ $=\displaystyle \frac{-6\pm 4\sqrt{5}}{2}$ $=-3\pm 2\sqrt{5}$ The points have coordinates $(0,-3-2\sqrt{5}) $ and $ (0,-3+2\sqrt{5})$
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