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8.1 Circle Terminology and Chord Properties This section will introduce you to some of the most important aspects of circle geometry Radius Diameter Tangent Chord

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Circumference The perimeter of a circle Radius A segment connecting the center of a circle with a point on the circle Diameter A segment that goes through the center of the circle and connects to two points on the outside of the circle Chord A segment whose end points are on the circle Tangent A line that intersects the circle on exactly one point

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The sum of the interior angles of a triangle is 180 The number of degrees in a circle is 360 Circumference = d = 2r Area of a circle = r 2 Pythagorean Theorem states that the sum of the squares of the legs of a right triangle is equal to the square of its hypotenuse a 2 + b 2 = c 2 180 360 a c b

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Formulas in Action Example 1: Find angle B Solution 1: -ABC is isoceles, so B = C -A + B + C = 180 -50 + B + B = 180 -2(B) = 130 -B = 65 A BC 50 C B A 12 5

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Some Important Chord Properties The Diameter perpendicular to a chord bisects the chord and its arc If AB CD, then CE = ED The perpendicular bisector of a chord passes through the center of the circle If AB CD and AE = EB, then CD passes through the center of the circle A E B DC A B C D E