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This guide explores the relationships between central angles, arcs, and triangles in circles, focusing on cases where the vertex is inside, on, or outside the circle. Each case is illustrated with examples that demonstrate how to find missing angle measures using relevant formulas and concepts, including properties of right triangles and the semicircle theorem. Perfect for students looking to enhance their understanding of geometry in circles and apply these concepts effectively in problem-solving scenarios.
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Central Angle Vertex OUTSIDE circle Vertex ON circle Vertex INSIDE circle Right Triangles
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Central Angle Vertex OUTSIDE circle Vertex ON circle Vertex INSIDE circle Right Triangles
Case I:Vertex is ON the circle ANGLE ARC ARC ANGLE
Ex. 1 Find m1. A B 1 124° C m1 = 62°
Ex. 2 Find m1. 1 84° m1 = 42°
Ex. 3 Find the value of x. x = 55°
Ex. 4 Find the mCADif mAB = 60. mCAD= 30°
Case II:Vertex is inside the circle A ARC B ANGLE D ARC C Looks like a PLUS sign!
Ex. 5 Find m1. 93° A B 1 D C 113° m1 = 103°
Ex. 6 Find mQT. mQT = 100° N Q 84° 92° M T
Case III:Vertex is outside the circle C ANGLE small ARC A D LARGE ARC B LARGE ARC LARGE ARC small ARC ANGLE small ARC ANGLE
Ex. 7 Find m1. 1 15° A D 65° B m1 = 25°
Ex. 8 Find mAB. mAB = 16° A 27° 70° B
Ex. 9 Find m1. 260° 1 m1 = 80°
Case IV:Triangle in a semicircle semicircle (180°) semicircle DIAMETER ANGLE ANGLE = 90°
Ex. 10 Find m1. AB is a diameter. m1 = 40° A 1 50° B
Ex. 11 Find m1. AB is a diameter. m1 = 46° A 1 88° C B
Case V:Central Angle ARC ANGLE = ARC ANGLE CENTER
Ex. 12 Find mAB. mAB= 32° C 32° B A
Ex. 13 Find mBC. AC is a diameter. mBC= 148° C 32° B A