Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Chapter 1 - Graphs - 1.4 Circles - 1.4 Assess Your Understanding - Page 38: 30

Answer

Center(3, -1); radius = 1 x-intercept = 3 No y-intercept

Work Step by Step

x² + y² - 6x + 2y + 9 = 0 (x² - 6x)+ (y² + 2y) + 9 = 0 (x² - 6x)+ (y² + 2y) + 9 - 9 = 0 - 9 Subtract 9 from both sides. (x² - 6x + 9)+ (y² + 2y + 1) = - 9 + 10 Complete the square of each expression in parenthesis. (x - 3)² + (y + 1)² = (1)² Compare this equation with the equation (x - h)² + (y - k)² = r². The comparison yields the information about the circle. We see that h = 3, k = - 1 and r = 1. To find the x-intercepts, if any, let y = 0 and solve for x. (x - 3)² + (0 + 1)² = (1)² (x - 3)² + 1 = 1 (x -3)² + 1 - 1 = 1 - 1 Subtract 1 from both sides. (x - 3)² = 0 x - 3 = 0 x - 3 + 3 = 0 + 3 x = 3 The x-intercept is 3. To find y-intercepts, if any, let x = 0 and solve for y. (0 - 3)² + (y + 1)² = 1 9 + (y + 1)² = 1 (y + 1)² + 9 - 9 = 1 - 9 Subtract 9 from both sides. (y + 1)² = - 8 y + 1 = ± √(-8) not real No real y-intercept exists.
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