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Math Notes » Geometry Vocabulary
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Geometry Vocabulary
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Vocabulary of Geometry * line segment - a line with two end points (the line ends at the points), it is named by its end points. example: line segment AB, line segment BA, or the letters AB with a line above it or BA with a line above it. * line - a line with no end points but has an arrow on each end because it goes on forever in both directions. It is named by its points. Example: line EF, line FE, or the letters EF with line above with arrows on each end or the letters FE with line above with arrows on each end. * ray - a line with one endpoint and an arrow on the other side, which goes on forever. It is named by the endpoint first, then the other point. Example: Ray CD, or the letters with a line above it and an arrow one one side. * plane - a flat surface that goes on forever on all sides. It is named by all points inside the plane. Example: Plane XYZ Look at book pages 306-307 for more information and examples. Angles Right angle - has a measure of exactly 90 degrees Obtuse angle - has a measure greater than 90 degrees and less than 180 degrees Acute angle - has a measure greater 0 degrees and less than 90 degrees Straight angle - has measure that equals 180 degrees There are several measurements that are benchmarks: 45 degrees, 90 degrees, 180 degrees, and 360 degrees (complete circle). Description of an Angle ** Remember it takes 2 rays to make an angle, one point that will match a point in each ray is going to be your vertex. Those two rays make the sides of the angle. The middle letter where the two rays meet is called the vertex. You can name an angle three ways, write the letters in order with the middle letter in the middle, write the letters going backwards but remember to keep the middle letter in the middle or just use the middle letter. However you chose to write them, make sure you use the symbol for angle at the beginning or the word angle. EX: Angle ABC, Angle CBA or Angle B Lines
parallel - two or more lines that run right next to each other and are exactly the same distance apart and never touch. perpendicular - two lines that touch or cross each other and form right angles. (looks like a plus sign or the capital letter T) intersecting - lines that cross at any point and DO NOT form right angles. Triangles
Classifying angles by their ANGLES acute triangle: contains three acute angles right triangle: contains one right angle obtuse triangle: contains one obtuse angle Classifying angles by their SIDES congruent: same shape and same size equilateral triangle: a triangle that has three congruent sides isosceles triangle: a triangle that has two congruent sides scalene triangle: a triangle that has no congruent sides
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