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Chapter 10 CIRCLES. Ms. Watson Geometry Banneker Academic High School. 10.1 Tangents to Circles. GOAL #1 Identify segments and lines related to circles. Who’s N’ The Circle Fam ?. radius. diameter. Who’s N’ The Circle Fam ?. secant. R. Q. tangent. P. S.
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Chapter 10CIRCLES Ms. Watson Geometry Banneker Academic High School
10.1 Tangents to Circles
Who’s N’ The Circle Fam? radius diameter
Who’s N’ The Circle Fam? secant R Q tangent P S
Who’s N’ The Circle Fam? Common External Tangent Common Internal Tangent Common Tangents A line or line segment that is tangent to two circles in the same plane is called a common tangent. 2 Types
Theorem 10.1 If a line is tangent to a circle, then it is perpendicular to the radius drawn to the point of tangency. What do we know about right triangles??? How can we use what we know to solve the length of sides of a triangle???
Theorem 10.3 If two segments from the same exterior point are tangent to a circle, then they are congruent (equal).
10.2 Arcs & Chords
Who’s N’ The Circle Fam? A Minor Arc C K Major Arc B
Name That Arc!Arcs are named by their endpoints. A Minor Arc C K Major Arc B
Measure That Arc! 60 ° 360° - 60 ° = 300 ° A Minor Arc 60 ° C 60 ° 300 ° K Major Arc B
Arc Addition PostulateDiscovery Step 1: Draw a circle. Step 2: Place three points on the circle named A, B, and C. Discover that… The measure of an arc formed by two adjacent arcs is the sum of the measures of the two arcs. mABC = mAB + mBC
Arc for Thought • Two arcs of the same circle or of congruent circles are congruent arcs if they have the same measure. So, two minor arcs of the same circle or of congruent circles are congruent if their central angles are congruent. Which minor arcs are congruent? Why are they congruent?
Theorem 10.4 A C B
Theorem 10.6 If one chord is a perpendicular bisector of another chord, the first chord is a diameter. J M K L
10.3 Inscribed Angles
Theorem 10.8 Measure of an Inscribed Angle If an angle is inscribed in a circle, then its measure is half the measure of its intercepted arc. m ABC = mAC A C B
Theorem 10.9 If two inscribed angles of a circle intercept the same are, then the angles are congruent. A C D B C D
Who’s N’ The Circle Fam? If all of the vertices of a polygon lie on a circle, the polygon is INSCRIBED in the circle and the circle is CIRCUMSCRIBED about the polygon.
Theorem 10.10 If a right triangle is inscribed in a circle, then the hypotenuse is a diameter of the circle. Also the angle opposite the diameter is a right angle. B is a right angle if and only if is a diameter of the circle. A B C
Theorem 10.11 A quadrilateral can be inscribed in a circle if and only if its opposite angles are supplementary. D, E, F, and G lie on the circle if and only if E F m D + m F = 180 And m E + m G = 180 G D