EXAMPLE 1 Use congruent chords to find an arc measure In the diagram, P Q, FG JK , and mJK = 80o. Find mFG SOLUTION Because FG and JK are congruent chords in congruent circles, the corresponding minor arcs FG and JK are congruent. So, mFG = mJK = 80o.
GUIDED PRACTICE for Example 1 Use the diagram of D. 1. If mAB = 110°, find mBC mBC = 110° ANSWER
GUIDED PRACTICE for Example 1 Use the diagram of D. 2. If mAC = 150°, find mAB mAB = 105° ANSWER
EXAMPLE 2 Use perpendicular bisectors Three bushes are arranged in a garden as shown. Where should you place a sprinkler so that it is the same distance from each bush? Gardening SOLUTION STEP 1 Label the bushes A, B, and C, as shown. Draw segments AB and BC .
EXAMPLE 2 Use perpendicular bisectors STEP 2 Draw the perpendicular bisectors of AB and BC By Theorem 10.4, these are diameters of the circle containing A, B, and C. STEP 3 Find the point where these bisectors intersect. This is the center of the circle through A, B, and C, and so it is equidistant from each point.
EXAMPLE 3 Use a diameter Use the diagram of E to find the length of AC . Tell what theorem you use. Diameter BD is perpendicular to AC . So, by Theorem 10.5, BD bisects AC , and CF = AF. Therefore, AC = 2 AF = 2(7) = 14. ANSWER
GUIDED PRACTICE for Examples 2 and 3 Find the measure of the indicated arc in the diagram. 3. CD mCD = 72° ANSWER
GUIDED PRACTICE for Examples 2 and 3 Find the measure of the indicated arc in the diagram. 4. DE mCD = mDE. mDE = 72° ANSWER 5. CE mCE = mDE + mCD mCE = 72° + 72° = 144° ANSWER
In the diagram of C, QR = ST = 16. Find CU. EXAMPLE 4 Use Theorem 10.6 In the diagram of C, QR = ST = 16. Find CU. SOLUTION Chords QR and ST are congruent, so by Theorem 10.6 they are equidistant from C. Therefore, CU = CV. CU = CV Use Theorem 10.6. 2x = 5x – 9 Substitute. x = 3 Solve for x. So, CU = 2x = 2(3) = 6.
GUIDED PRACTICE for Example 4 In the diagram in Example 4, suppose ST = 32, and CU = CV = 12. Find the given length. 6. QR QR = 32 ANSWER
GUIDED PRACTICE for Example 4 In the diagram in Example 4, suppose ST = 32, and CU = CV = 12. Find the given length. 7. QU QU = 16 ANSWER
GUIDED PRACTICE for Example 4 In the diagram in Example 4, suppose ST = 32, and CU = CV = 12. Find the given length. 8. The radius of C ANSWER The radius of C = 20
Daily Homework Quiz 1. Find the value of x in C. Explain. . ANSWER 6; If a diameter of a circle is to the chord, then the diameter bisects the chord and its arc.
Daily Homework Quiz Find the value of x in C. Explain. . 2. ANSWER 4; In the same circle, if two chords are equidistant from the center, then they are . = ~
Daily Homework Quiz 3. Determine whether RS is a diameter. ANSWER Yes. Sample answer: RS is the bisector of TU by Theorem 5.3. Then RS is a diameter of the circle by Theorem 10.4.