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# Chapter Seven

### Proportions and Similarity

Term | Definition |
---|---|

ratio | comparison of two quantities using division |

extended ratio | Used to compare 3 or more quantities, a:b:c |

proportion | an equation that states two ratios are equal |

cross products property | In a proportion, the product of the extremes equals the products of the means |

Equivalent Proportions | a/b=c/d; b/a=d/c; a/c=b/d; c/a=d/b |

similar polygons | 2 polygons are similar if and only if their corresponding angles are congruent and corresponding side lengths are proportional. |

scale factor | The ratio of the lengths of the corresponding sides of 2 similar polygons. It depends upon the order of comparison. |

Similarity and Congruence | If two polygons are congruent, they are similar. All of the corresponding angles are congruent and the lengths of the corresponding sides have a ratio of 1:1 |

Identifying Similar Triangles | When only 2 congruent angles of a triangle are given, remember you can use the THIRD ANGLE THEOREM to establish that the remaining corresponding angles are also congruent. |

midsegment of a triangle | segment with endpoints that are the midpoints of two sides of the triangle. Every triangle has 3 midsegments. |

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amgeometry