LESSON A: DEFINING CIRCLES & THEIR PARTS 4/16/2017 Geometry/McConaughy

In this lesson, you will define circles and their parts. 4/16/2017 Geometry/McConaughy

VOCABULARY Circle- in a plane, the set of all points that are a given distance (radius) from a common point (center) 4/16/2017 Geometry/McConaughy

VOCABULARY RADIUS Circles are named by their centers. O O a segment from the center of a circle to a point on the circle radius -________________________________ ______________________________________ 4/16/2017 Geometry/McConaughy

VOCABULARY Concentric circles- two or more circles which share the same center Congruent circles- two circles which have radii of the same length 3 in. 3 in. 4/16/2017 Geometry/McConaughy

VOCABULARY NOTE: Radii, chords, and diameters are all segments in a circle. CHORD -____________________________________ segment in a circle with endpoints on the circle DIAMETER -____________________________________ chord which intersects a circle’s center 4/16/2017 Geometry/McConaughy

NOTE: Tangents and secants are lines of a circle . VOCABULARY TANGENT TANGENT -____________________________________ __________________ Point of Tangency line which intersects a circle in exactly one point SECANT -____________________________________ __________________ line which intersects a circle in exactly two points SECANT 4/16/2017 Geometry/McConaughy

VOCABULARY NOTE: Central angles and inscribed angles are angles of a circle. VOCABULARY CENTRAL ANGLE -____________________________________ __________________ angle with its vertex at the center and its legs (sides) two radii of the circle INSCRIBED ANGLE -____________________________________ __________________ __________________ __________________ an angle with all points on the circle and legs (sides) two chords of the circle 4/16/2017 Geometry/McConaughy

An arc of a circle is two points on a circle and the continuous (unbroken) part of the circle between the two points. Arc 4/16/2017 Geometry/McConaughy

Classifying Arcs: NOTE: Semicircles, major arcs, and minor arcs are arcs of a circle. SEMICIRCLE -____________________________________ __________________ Name two semicircles. an arc of a circle whose endpoints are the endpoints of a diameter Name five minor arcs. Name two major arcs. MINOR ARC -____________________________________ arc smaller than a semicircle MAJOR ARC -____________________________________ arc larger than a semicircle 4/16/2017 Geometry/McConaughy

FINAL CHECKS FOR UNDERSTANDING: Always use correct symbols for segments, lines, angles, and arcs when naming circle parts. FINAL CHECKS FOR UNDERSTANDING: Name the following circles parts, then distinguish among/between those in each category: SEGMENTS IN CIRCLES LINES IN CIRCLES ANGLES IN ARCS IN CIRCLES radius tangent central angle semicircle diameter secant minor arc chord inscribed angle major arc 4/16/2017 Geometry/McConaughy

Homework: Circle Parts WS 4/16/2017 Geometry/McConaughy