218 CHAPTER 2 Graphs and Functions CONCEPT PREVIEW Answer each question. 9. How many points lie on the graph of x2 + y2 = 0? 10. How many points lie on the graph of x2 + y2 = -100? CONCEPT PREVIEW Match each equation in Column I with its graph in Column II. I 5. 1x - 322 + 1y - 222 = 25 6. 1x - 322 + 1y + 222 = 25 7. 1x + 322 + 1y - 222 = 25 8. 1x + 322 + 1y + 222 = 25 II A. 0 –2 –3 x y B. 0 2 3 x y C. 0 3 –2 x y D. 0 2 –3 x y In the following exercises, (a) find the center-radius form of the equation of each circle described, and (b) graph it. See Examples 1 and 2. 11. center 10, 02, radius 6 12. center 10, 02, radius 9 13. center 12, 02, radius 6 14. center 13, 02, radius 3 15. center 10, 42, radius 4 16. center 10, -32, radius 7 17. center 1-2, 52, radius 4 18. center 14, 32, radius 5 19. center 15, -42, radius 7 20. center 1-3, -22, radius 6 21. center A 22, 22 B, radius 22 22. center A -23, -23 B, radius 23 Connecting Graphs with Equations Use each graph to determine an equation of the circle in (a) center-radius form and (b) general form. 23. (1, 1) (5, 1) (3, –1) (3, 3) x y 0 24. (–1, –5) (–4, –2) (2, –2) (–1, 1) x y 0 25. (–4, 2) (0, 2) (–2, 0) (–2, 4) x y 0 26. (3, –6) (6, –3) (0, –3) (3, 0) x y 0
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