10.3 Using hords ssential uestion What are two ways to determine when a chord is a diameter of a circle? rawing iameters OOKI O UU o be proficient in math, you need to look closely to discern a pattern or structure. Work with a partner. Use dynamic geometry software to construct a circle of radius 5 with center at the origin. raw a diameter that has the given point as an endpoint. xplain how you know that the chord you drew is a diameter. a. (4, 3) b. (0, 5) c. ( 3, 4) d. ( 5, 0) Work with a partner. Use dynamic geometry software to construct a chord of a circle. onstruct a chord on the perpendicular bisector of. What do you notice? hange the original chord and the circle several times. re your results always the same? Use your results to write a conjecture. Writing a onjecture about hords hord erpendicular to a iameter Work with a partner. Use dynamic geometry software to construct a diameter of a circle. hen construct a chord perpendicular to at point. ind the lengths and. What do you notice? hange the chord perpendicular to and the circle several times. o you always get the same results? Write a conjecture about a chord that is perpendicular to a diameter of a circle. ommunicate Your nswer 4. What are two ways to determine when a chord is a diameter of a circle? ection 10.3 Using hords 589
10.3 esson What You Will earn ore Vocabulary revious chord arc diameter I If, then the point, and any line, segment, or ray that contains, bisects. Use chords of circles to find lengths and arc measures. Using hords of ircles ecall that a chord is a segment with endpoints on a circle. ecause its endpoints lie on the circle, any chord divides the circle into two arcs. diameter divides a circle into two semicircles. ny other chord divides a circle into a minor arc and a major arc. heorems ongruent orresponding hords heorem In the same circle, or in congruent circles, two minor arcs are congruent if and only if their corresponding chords are congruent. roof x. 19, p. 594 semicircle diameter semicircle major arc chord minor arc if and only if. bisects. erpendicular hord isector heorem If a diameter of a circle is perpendicular to a chord, then the diameter bisects the chord and its arc. roof x. 22, p. 594 If is a diameter and, then and. erpendicular hord isector onverse If one chord of a circle is a perpendicular bisector of another chord, then the first chord is a diameter. roof x. 23, p. 594 If is a perpendicular bisector of, then is a diameter of the circle. Using ongruent hords to ind an rc Measure In the diagram,, JK, J and m JK = 80. ind m. 80 K OUIO ecause and JK are congruent chords in congruent circles, the corresponding minor arcs and JK are congruent by the ongruent orresponding hords heorem. o, m = m JK = 80. 590 hapter 10 ircles
Using a iameter a. ind K. b. ind m K. 11x OUIO a. iameter J is perpendicular to K. o, by the erpendicular hord isector heorem, J bisects K, and = K. J (70 + x) K 7 o, K = 2(K) = 2(7) = 14. b. iameter J is perpendicular to K. o, by the erpendicular hord isector heorem, J bisects K, and m J = m JK. m J = m JK erpendicular hord isector heorem 11x = (70 + x) ubstitute. 10x = 70 ubtract x from each side. x = 7 ivide each side by 10. o, m J = m JK = (70 + x) = (70 + 7) = 77, and m K = 2(m J ) = 2(77 ) = 154. Using erpendicular isectors hree bushes are arranged in a garden, as shown. Where should you place a sprinkler so that it is the same distance from each bush? OUIO tep 1 tep 2 tep 3 M sprinkler abel the bushes,, and, as shown. raw segments and. raw the perpendicular bisectors of and. y the erpendicular hord isector onverse, these lie on diameters of the circle containing,, and. ind the point where the perpendicular bisectors intersect. his is the center of the circle, which is equidistant from points,, and. Monitoring rogress In xercises 1 and 2, use the diagram of. 1. If m = 110, find m. 2. If m = 150, find m. In xercises 3 and 4, find the indicated length or arc measure. 3. 4. m elp in nglish and panish at igideasmath.com 5 9x (80 x) 9 9 ection 10.3 Using hords 591
heorem quidistant hords heorem In the same circle, or in congruent circles, two chords are congruent if and only if they are equidistant from the center. roof x. 25, p. 594 if and only if =. Using ongruent hords to ind a ircle s adius W U 2x 5x 9 Y V X In the diagram, = = 16, U = 2x, and V = 5x 9. ind the radius of. OUIO ecause is a segment whose endpoints are the center and a point on the circle, it is a radius of. ecause U, U is a right triangle. pply properties of chords to find the lengths of the legs of U. W U 2x radius 5x 9 Y V X tep 1 ind U. ecause and are congruent chords, and are equidistant from by the quidistant hords heorem. o, U = V. U = V quidistant hords heorem 2x = 5x 9 ubstitute. x = 3 olve for x. o, U = 2x = 2(3) = 6. tep 2 ind U. ecause diameter WX, WX bisects by the erpendicular hord isector heorem. o, U = 1 (16) = 8. 2 J 3x K 7x 12 M tep 3 ind. ecause the lengths of the legs are U = 6 and U = 8, U is a right triangle with the ythagorean triple 6, 8, 10. o, = 10. o, the radius of is 10 units. Monitoring rogress elp in nglish and panish at igideasmath.com 5. In the diagram, JK = M = 24, = 3x, and = 7x 12. ind the radius of. 592 hapter 10 ircles
10.3 xercises ynamic olutions available at igideasmath.com Vocabulary and ore oncept heck 1. WII escribe what it means to bisect a chord. 2. WII wo chords of a circle are perpendicular and congruent. oes one of them have to be a diameter? xplain your reasoning. Monitoring rogress and Modeling with Mathematics In xercises 3 6, find the measure of the red arc or chord in. (ee xample 1.) 3. 5. 110 Z 60 75 W Y X 120 4. 34 5 U 34 V 6. 7 (5x + 2) (7x 12) 7 120 11 In xercises 7 10, find the value of x. (ee xample 2.) 7. 9. M J 8 x 5x 6 10. 2x + 9 8. U x 40 11. O YI escribe and correct the error in reasoning. ecause bisects,. M 12. OM OVI In the cross section of the submarine shown, the control panels are parallel and the same length. escribe a method you can use to find the center of the cross section. Justify your method. (ee xample 3.) In xercises 13 and 14, determine whether is a diameter of the circle. xplain your reasoning. 13. 14. 3 3 In xercises 15 and 16, find the radius of. (ee xample 4.) 15. 16 16. 4x + 4 4x + 3 7x 6 16 ection 10.3 Using hords 593 5 5 5 6x 6 17. OM OVI n archaeologist finds part of a circular plate. What was the 7 in. diameter of the plate to the nearest tenth of an 7 in. inch? Justify your answer. 6 in. 6 in.
18. OW O YOU I? What can you conclude from each diagram? ame a theorem that justifies your answer. a. c. J b. d. 90 90 19. OVI OM Use the diagram to prove each part of the biconditional in the ongruent orresponding hords heorem. a. iven and are congruent chords. rove b. iven rove 20. MMI OIO In, all the arcs shown have integer measures. how that x must be even. x M 22. OVI OM Use congruent triangles to prove the erpendicular hord isector heorem. iven is a diameter of. rove, 23. OVI OM Write a proof of the erpendicular hord isector onverse. iven is a perpendicular bisector of. rove is a diameter of the circle. (int: lot the center and draw and.) 24. OU OVOKI onsider two chords that intersect at point. o you think that =? Justify your answer. 25. OVI OM Use the diagram with the quidistant hords heorem on page 592 to prove both parts of the biconditional of this theorem. 26. MKI UM car is designed so that the rear wheel is only partially visible below the body of the car. he bottom edge of the panel is parallel to the ground. Your friend claims that the point where the tire touches the ground bisects. Is your friend correct? xplain your reasoning. 21. OI In, the lengths of the parallel chords are 20, 16, and 12. ind m. xplain your reasoning. Maintaining Mathematical roficiency ind the missing interior angle measure. (ection 7.1) eviewing what you learned in previous grades and lessons 27. uadrilateral JKM has angle measures m J = 32, m K = 25, and m = 44. ind m M. 28. entagon has angle measures m = 85, m = 134, m = 97, and m = 102. ind m. 594 hapter 10 ircles