Chapter 5 Plane Geometry
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42 terms
Terms | Definitions |
|---|---|
 point | names a location |
| line | perfectly straight and extends forever in both directions |
| plane | perfectly flat surface that extends forever in all directions |
| segment | the part of a line between two points |
| ray | part of a line that starts at one point and extends forever in one direction |
| angle | formed by two rays with a common endpoint called the vertex |
| right angle | measures 90º |
| acute angle | measures less than 90º |
| obtuse angle | measures greater than 90º |
| complementary angles | measures that add to 90º |
| supplementary angles | measures that add to 180º |
| parallel lines | two lines in a plane that never meet |
| perpendicular lines | two lines that intersect at 90º angles |
| transversal | a line that intersects any two or more other lines |
| Properties of Transversals to Parallel lines | the acute angles that are formed are all congruent; the obtuse angles are all congruent; any acute angle is supplementary to any obtuse angle. |
| Triangle Sum Theorem | The angle measures of a triangle in a plane add to 180 degrees |
| acute triangle | 3 acute angles |
| Right triangle | 1 right angle |
| equilateral triangle | 3 congruent sides and 3 congruent angles |
| isosceles triangle | at least 2 congruent sides and 2 congruent angles |
| scalene triangle | no congruent sides and no congruent angles |
| polygon | a closed plane figure formed by three or more segments |
| regular polygon | a polygon where all sides and angles have equal measure |
| trapezoid | exactly 1 pair of parallel sides |
| parallelogram | has 2 pairs of parallel sides |
| rectangle | has 4 right angles |
| rhombus | has 4 congruent sides |
| square | 4 congruent sides and 4 right angles |
| slope | a number that describes how steep a line is |
| rise | vertical change |
| run | horizontal change |
| correspondence | a way of matching up two sets of objects |
| transformation | translations, rotations, reflections |
| translation | slides a figure along a line without turning |
| rotation | turns the figure around a point called the center of rotation |
| reflection | flips the figure across a line to create a mirror image |
| line symmetry | a line through an image so that the two sides are mirror images |
| Line of Symmetry | the name of the line used in line symmetry |
| tessellation | a repeating pattern of plane figures that completely covers a plane with no gaps or overlaps |
| regular tessellation | a regular polygon is repeated to fill a plane. The angles at each vertex add to 360º |
| semiregular tessellation | two or more regular polygons are repeated to fill the plane and the vertices are all identical. |
| Obtuse triangle | Has one obtuse angle |
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