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Learn about inscribed angles in circles and how to find angle measures using the Inscribed Angle Theorem. Discover proofs, real-world examples, and applications. Master the concepts through examples and two-column proofs.
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Five-Minute Check (over Lesson 10–3) NGSSS Then/Now New Vocabulary Theorem 10.6: Inscribed Angle Theorem Proof: Inscribed Angle Theorem (Case 1) Example 1: Use Inscribed Angles to Find Measures Theorem 10.7 Example 2: Use Inscribed Angles to Find Measures Example 3: Use Inscribed Angles in Proofs Theorem 10.8 Example 4: Find Angle Measures in Inscribed Triangles Theorem 10.9 Example 5: Real-World Example: Find Angle Measures Lesson Menu
A B C D A. 60 B. 70 C. 80 D. 90 5-Minute Check 1
A B C D A. 40 B. 45 C. 50 D. 55 5-Minute Check 2
A B C D A. 40 B. 45 C. 50 D. 55 5-Minute Check 3
A B C D A. 40 B. 30 C. 25 D. 22.5 5-Minute Check 4
A B C D A. 24.6 B. 26.8 C. 28.4 D. 30.2 5-Minute Check 5
A B C D A. B. C. D. 5-Minute Check 6
MA.912.G.6.1Determine the center of a given circle. Given three points not on a line, construct the circle that passes through them. Construct tangents to circles. Circumscribe and inscribe circles about and within triangles and regular polygons. MA.912.G.6.4 Determine and use measures of arcs and related angles. Also addresses MA.912.G.6.3. NGSSS
You found measures of interior angles of polygons. (Lesson 6–1) • Find measures of inscribed angles. • Find measures of angles of inscribed polygons. Then/Now
inscribed angle • intercepted arc Vocabulary
Use Inscribed Angles to Find Measures A. Find mX. Answer:mX = 43 Example 1
B. Use Inscribed Angles to Find Measures = 2(252) or 104 Example 1
A B C D A. Find mC. A. 47 B. 54 C. 94 D. 188 Example 1
A B C D B. A. 47 B. 64 C. 94 D. 96 Example 1
RS R and S both intercept . Use Inscribed Angles to Find Measures ALGEBRA Find mR. mRmS Definition of congruent angles 12x – 13 = 9x + 2 Substitution x = 5 Simplify. Answer:So, mR = 12(5) – 13 or 47. Example 2
A B C D ALGEBRA Find mI. A. 4 B. 25 C. 41 D. 49 Example 2
Write a two-column proof. Given: Prove: ΔMNP ΔLOP Proof: Statements Reasons LO MN2. If minor arcs are congruent, then corresponding chords are congruent. Use Inscribed Angles in Proofs 1.Given Example 3
Proof: Statements Reasons M intercepts and L intercepts . 3. Definition of intercepted arc Use Inscribed Angles in Proofs M L4. Inscribed angles of the same arc are congruent. MPN OPL 5. Vertical angles are congruent. ΔMNP ΔLOP 6. AAS Congruence Theorem Example 3
Write a two-column proof. Given: Prove: ΔABE ΔDCE Select the appropriate reason that goes in the blank to complete the proof below. Proof: Statements Reasons AB DC2. If minor arcs are congruent, then corresponding chords are congruent. 1.Given Example 3
Proof: Statements Reasons D intercepts and A intercepts . 3. Definition of intercepted arc D A4. Inscribed angles of the same arc are congruent. DEC BEA 5. Vertical angles are congruent. ΔDCE ΔABE 6. ____________________ Example 3
A B C D A. SSS Congruence Theorem B. AAS Congruence Theorem C. Definition of congruent triangles D. Definition of congruent arcs Example 3
Find Angle Measures in Inscribed Triangles ALGEBRA Find mB. ΔABC is a right triangle because C inscribes a semicircle. mA + mB + mC = 180Angle Sum Theorem (x + 4) + (8x – 4) + 90 = 180 Substitution 9x + 90 = 180 Simplify. 9x = 90 Subtract 90 from each side. x = 10 Divide each side by 9. Answer:So, mB = 8(10) – 4 or 76. Example 4
A B C D ALGEBRA Find mD. A. 8 B. 16 C. 22 D. 28 Example 4
Find Angle Measures INSIGNIAS An insignia is an emblem that signifies rank, achievement, membership, and so on. The insignia shown is a quadrilateral inscribed in a circle. Find mS and mT. Example 5
Find Angle Measures Since TSUV is inscribed in a circle, opposite angles are supplementary. S + V = 180S + V = 180 S + 90= 180 (14x) + (8x + 4) = 180 S = 90 22x + 4 = 180 22x = 176 x = 8 Answer:So, mS = 90 and mT = 8(8) + 4 or 68. Example 5
A B C D INSIGNIAS An insignia is an emblem that signifies rank, achievement, membership, and so on. The insignia shown is a quadrilateral inscribed in a circle. Find mN. A. 48 B. 36 C. 32 D. 28 Example 5