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Circle G E O M E T R Y. Radius (or Radii for plural). The segment joining the center of a circle to a point on the circle. Example: OA. Diameter. A chord that passes through the center of a circle. Example: AB. Chord. A segment joining two points on a circle Example: AB. Chord.
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Radius (or Radii for plural) • The segment joining the center of a circle to a point on the circle. • Example: OA
Diameter • A chord that passes through the center of a circle. • Example: AB
Chord • A segment joining two points on a circle • Example: AB
Chord • A segment joining two points on a circle • Example: AB
Secant • A line that intersects the circle at exactly two points. • Example: AB
Tangent • A line that intersects a circle at exactly one point. • Example: AB
Arc • A figure consisting of two points on a circle and all the points on the circle needed to connect them by a single path. • Example: arc AB
Central Angle • An angle whose vertex is at the center of a circle. • Example: Angle ABC
Central angles will always equal the inscribed arc. • Example: angle ABC = arc AC
Example 2 • Find the measures of the red arcs. Are the arcs congruent?
Example 1 • Find the measure of each arc. 70° 360° - 70° = 290° 180°
Inscribed Angle • An angle whose vertex is on a circle and whose sides are determined by two chords. • Example: Angle ABC
Intercepted Arc • An arc that lies in the interior of an inscribed angle. • Example: arc AC
An inscribed arc will always equal twice the inscribed angle. • Ex. Arc AC= 2 times Angle ABC
Example 1 • Find the measure of the blue arc or angle. a. b.
Example 1 • Tell whether the line or segment is best described as a chord, a secant, a tangent, a diameter, or a radius. tangent diameter chord radius
Tangent Theorem • The tangent is a line or line segment that touches the perimeter of a circle at one point only and is perpendicular to the radius that contains the point.
Example 3 Use the converse of the Pythagorean Theorem to see if the triangle is right. 112 + 432 ? 452 121 + 1849 ? 2025 1970 2025
Definitions • Inscribed polygon – a polygon whose vertices all lie on a circle. • Circumscribed circle – A circle with an inscribed polygon. The polygon is an inscribed polygon and the circle is a circumscribed circle.
Inscribed Quadrilateral • If a quadrilateral is inscribed in a circle, then both pairs of opposite angles are supplementary.
Inscribed Right Triangle Theorem • If a right triangle is inscribed in a circle, then the hypotenuse is a diameter of the circle. Conversely, if one side of an inscribed triangle is a diameter of the circle, then the triangle is a right triangle and the angle opposite the diameter is the right angle.
Example 3 • Find the value of each variable. b. a.
Chord Product Theorem • If two chords intersect in the interior of a circle, then the product of the lengths of the segments of one chord is equal to the product of the lengths of the segments of the other chord.
Example 1 • Find the value of x.
Try This! • Find the value of x.