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Parts of a Circle Circle – set of all points _________ from a given point called the _____ of the circle (in a plane). equidistant C center Symbol: C
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CHORD: a segment whose ________ are on the circle
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RADIUS: distance from the _____ to a point on the circle
center P
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DIAMETER: distance ______ the circle through its ______
across P center Also known as the longest chord.
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What is the relationship between the diameter and the radius of a circle?
OR D = ½ D 2 r
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D = ? 24 32 12 r = ? 16 r = ? 4.5 6 D = ? 12 9
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Use P to determine whether each statement is true or false.
Q R T S
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SECANT sounds like second
Secant Line A secant line intersects the circle at exactly TWO points. SECANT sounds like second
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TANGENT: a LINE that intersects the circle exactly ONE time
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Point of Tangency
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Secant Radius Diameter Chord Tangent
Name the term that best describes the line. Secant Radius Diameter Chord Tangent
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Two circles can intersect…
in two points one point or no points
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No points of intersection (different center)
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No points of intersection (same center)
Concentric Circles Same center but different radii
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1 point of intersection (Tangent Circles)
Externally Tangent Internally Tangent
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2 points of intersection
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Common Tangents Internal
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Common Tangents External
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Place the following words on post-its
Secant Radius Diameter Chord Tangent Center Point of Tangency Have students come up and put the post it on the part of the circle. Like pin the tail on the donkey (but with eyes open!)
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Your text here
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Secant Radius Center Diameter Chord Point of Tangency Tangent
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Students will only have 30 seconds to answer
2 students will come to the front of the class. One has their back to the screen (the guesser), the other is facing the screen (the clue giver) The clue giver will have to give clues to the guesser to get them to guess the word. They may draw a picture as a clue. He/she may NOT say ANY part of the word during clue giving Students will only have 30 seconds to answer If the guesser is correct they become the clue giver and the clue giver gets to choose a new student to be the guesser If the guesser is wrong, they must do another word You can make this more challenging by playing ‘taboo’ rules where the person describing the word is restricted from saying certain words as a clue. For example on for semi circle they might not be allowed to say “half” That challenges students to think of other words to describe a semicircle like maybe “180 degrees.” I included taboo words on the notes for each word
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Semicircle Half
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Chord line
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Secant Line through
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Major Arc Big minor
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Inscribed Angle circle
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Diameter line
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Central Angle middle
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Tangent Line touch
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Minor Arc Major small
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Radius Center diameter
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<APB is a Central Angle
Central Angle : An Angle whose vertex is at the center of the circle A Major Arc Minor Arc More than 180° Less than 180° ACB P AB To name: use 3 letters C To name: use 2 letters B <APB is a Central Angle
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Semicircle: An Arc that equals 180°
To name: use 3 letters E D EDF P F
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THINGS TO KNOW AND REMEMBER ALWAYS
A circle has 360 degrees A semicircle has 180 degrees Vertical Angles are Congruent
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measure of an arc = measure of central angle
96 Q m AB = 96° B C m ACB = 264° m AE = 84°
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Arc Addition Postulate
B m ABC = + m BC m AB
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240 260 m DAB = m BCA = Tell me the measure of the following arcs. D
140 260 m BCA = R 40 100 80 C B
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CONGRUENT ARCS Congruent Arcs have the same measure and MUST come from the same circle or of congruent circles. C B D 45 45 110 A
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