Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 1 - Section 1.9 - The Coordinate Plane; Graphs of Equations; Circles - 1.9 Exercises - Page 104: 103

Answer

The equation given represents a circle of center $\Big(\dfrac{3}{4},0\Big)$ and radius $\dfrac{3}{4}$

Work Step by Step

$2x^{2}+2y^{2}-3x=0$ Take out common factor $2$ from the left side of the equation: $2\Big(x^{2}+y^{2}-\dfrac{3}{2}x\Big)=0$ Take $2$ to divide the right side: $x^{2}+y^{2}-\dfrac{3}{2}x=\dfrac{0}{2}$ $x^{2}+y^{2}-\dfrac{3}{2}x=0$ Group the terms with $x$ together and group the terms with $y$ together: $\Big(x^{2}-\dfrac{3}{2}x\Big)+y^{2}=0$ Complete the square for the first parentheses. Add $\Big(\dfrac{b}{2}\Big)^{2}$ inside the parentheses and do the same on the right side of the equation. In this particular case, $b=-\dfrac{3}{2}$. $\Big[x^{2}-\dfrac{3}{2}x+\Big(-\dfrac{3}{2\cdot2}\Big)^{2}\Big]+y^{2}=\Big(-\dfrac{3}{2\cdot2}\Big)^{2}$ $\Big(x^{2}-\dfrac{3}{2}x+\dfrac{9}{16}\Big)+y^{2}=\dfrac{9}{16}$ Factor the expression inside the parentheses, which is a perfect square trinomial: $\Big(x-\dfrac{3}{4}\Big)^{2}+y^{2}=\dfrac{9}{16}$ The expression obtained is the equation of a circle in $(x-h)^{2}+(y-k)^{2}=r^{2}$ form, where $\Big(\dfrac{3}{4},0\Big)$ is the center of the circle and $\dfrac{3}{4}$ is its radius.
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