Aim #18: How can we work with the properties of tangents ...



The Bronx High School of Science Math Department

Valerie Reidy, Principal R. Jahoda, A.P.

Name:_______________________________ Date:____________ Period:________

M4 Teacher: Ms. Zinn

Formulas for Determining Angle Measures

(use p377 of the Amsco Review Book to help you)

|Type of Angle |Identifying Elements |Diagram |Formula |

|Central Angle | |[pic] | |

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|Inscribed angle | | | |

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|Angle formed by a tangent and a chord| | | |

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|Angle formed by a secant and a chord | | | |

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|Angle formed by two chords | | | |

|intersecting within a circle | | | |

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|Angle formed by a tangent and a | | | |

|radius | | | |

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|Type of Angle |Identifying Elements |Diagram |Formula |

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|Angle formed by two secants | | | |

|intersecting outside the circle | | | |

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|Angle formed by a secant and a tangent| | | |

|intersecting outside the circle | | | |

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|Angle formed by two tangent | | | |

|intersecting outside of the circle | | | |

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[pic]

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Some theorems used in Circle proofs:

1) In a circle, all radii are congruent.

2) In a circle, if two central angles are congruent, then their intercepted arcs are congruent.

3) In a circle, if two chords are congruent, then the arcs they intercept are congruent

4) In a circle, if two arcs are congruent, then the chords that form them are congruent.

5) If a radius (diameter) is perpendicular to a chord, then it bisects the chord and its arcs.

6) In a circle, if two chords are congruent, then they are equidistant from the center of the circle.

7) If an angle is inscribed in a semicircle, then it is a right angle.

8) If two inscribed angles intercept the same arc, then they are congruent.

9) If two chords in a circle are parallel, then they intercept congruent arcs between them.

10) If a line is tangent to a circle, then it is perpendicular to the radius at that point.

11) If two tangent segments are drawn to a circle from an external point, they are congruent.

THESE ARE NOT ALL OF THE THEOREMS WE HAVE SPOKEN ABOUT!

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