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# Grade 7 Chapter 7

### Foundations for Geometry

Question | Answer |
---|---|

acute angle | An angle that measures less than 90 degrees. |

acute triangle | A triangle with all angles measuring less than 90 degrees. |

angle | A figure formed by two rays with a common vertex. |

center of rotation | The point about which a figure is rotated. |

complementary angles | Two angles whose measures add up to 90 degrees. |

congruent | Having the same size and shape. |

correspondence | The relationship between two or more objects that are matched. |

equilateral triangle | A triangle with three congruent sides. |

image | A figure resulting from a transformation. |

isosceles triangle | A triangle with at least two congruent sides. |

line | A straight path that extends without end in opposite directions. |

line of symmetry | the imaginary "mirror" in line symmetry. |

line symmetry | One half of a figure is a mirror image of the other half. |

obtuse angle | An angle whose measure is greater that 90 degrees but less than 180 degrees. |

obtuse triangle | A triangle containing one obtuse angle. |

parallel lines | Lines in a plane that do not intersect. |

parallelogram | A quadrilateral with two pairs of parallel sides. |

perpendicular lines | Lines that intersect to form right angles. |

plane | A flat surface that extends forever. |

point | An exact location in space. |

polygon | A close plane figure formed by three or more line segments that intersect only at their endpoints. |

ray | A part of a line that starts at one endpoint and extends forever. |

rectangle | A parallelogram with four right angles. |

reflection | A transformation of a figure that flips the figure across a line. |

regular polygon | A polygon with congruent sides and angles. |

regular tessellation | A regular polygon is repeated to fill a plane. |

rhombus | A parallelogram with all sides congruent. |

right angle | An angle that measures 90 degrees. |

right triangle | A triangle containing a right angle. |

rise | The vertical change when,the slope of a line is expressed as the ratio rise/run, or "rise over run". |

rotation | A transformation in which a figure is turned around a point. |

rotational symmetry | When a figure can be rotated less than 360 degrees around a central point and coincides with the original figure. |

run | The horizontal change when,the slope of a line is expressed as the ratio rise/run, or "rise over run". |

scalene triangle | A triangle with no congruent sides. |

segment | A part of a line between two endpoints. |

slope | A measure of the steepness of a line on a graph; the rise divided by the run. |

square | A rectangle with four congruent sides. |

supplementary angles | Two angles whose measures have a sum of 180 degrees. |

tessellation | A repeating pattern of plane figures that completely cover a plane with no gaps or overlaps. |

transformation | A change in the size or position of a figure. |

translation | A movement (slide) of a figure along a straight line. |

transversal | A line that intersects two or more lines. |

trapezoid | A quadrilateral with exactly one pair of parallel sides. |

Triangle Sum Theorem | The measures of the angles in a triangle add up to 180 degrees. |

vertical angles | A pair of opposite congruent angles formed by intersecting lines. |

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