1. Angles Related to a Circle Lesson 10.5

2. Inscribed Angle: an angle whose vertex is on a circle and whose sides are determined by two chords. • Tangent-Chord Angle: Angle whose vertex is on a circle whose sides are determined by a tangent and a chord that intersects at the tangent’s point of contact. • Theorem 86: The measure of an inscribed angle or a tangent-chord angle (vertex on circle) is ½ the measure of its intercepted arc. Angles with Vertices on a Circle

4. Angles with Vertices Inside, but NOT at the Center of, a Circle. Definition:A chord-chord angle is an angle formed by two chords that intersect inside a circle but not at the center. Theorem 87:The measure of a chord-chord angle is one-half the sum of the measures of the arcs intercepted by the chord-chord angle and its vertical angle.

5. ½ a = 65 a = 130 x = ½ (88 + 27) x = 57.5º

6. ½ (21 + y) = 72 21 + y = 144 y = 123º

7. Find y. Find mBEC. mBEC = ½ (29 + 47) mBEC = 38º y = 180 – mBEC y = 180 – 38 = 142º

8. Part 2 of Section 10.5…

9. Angles with Vertices Outside a Circle Three types of angles… 1. A secant-secant angle is an angle whose vertex is outside a circle and whose sides are determined by two secants.

10. Angles with Vertices Outside a Circle 2. A secant-tangent angle is an angle whose vertex is outside a circle and whose sides are determined by a secant and a tangent.

11. Angles with Vertices Outside a Circle 3. A tangent-tangent angle is an angle whose vertex is outside a circle and whose sides are determined by two tangents. Theorem 88: The measure of a secant-secant angle, a secant-tangent angle, or a tangent-tangent angle (vertex outside a circle) is ½ the difference of the measures of the intercepted arcs.

12. y = ½ (57 – 31) y = ½(26) y = 13 ½ (125 – z) = 32 125 – z = 64 z = 61

13. First find the measure of arc EA. m of arc AEB = 180 so arc EA = 180 – (104 + 20) = 56 . mC = ½ (56 – 20) mC = 18

14. ½ (x + y) = 65 and ½ (x – y ) = 24 x + y = 130 and x – y = 48 x + y = 130 x – y = 48 2x = 178 x = 89 89 + y = 130 y = 41