Vocabulary 2.1

1. Vocabulary 2.1 MA418 – Spring 2010 McAllister

2. Point • Location in space that has no size or dimension • Is usually denoted by a dot and a capital letter • Example .A

3. Line • An infinite set of points that can be determined by any two of those points. • Denoted by ↔ over two of the points on the line. • ↔AB

4. Plane • An infinite set of points that can be uniquely determined by at least 3 non-collinear points. • Note: collinear means points that are on the same line, non-collinear means points that are not all on the same line.

5. Line segment • A subset of the points on a line that consists of 2 given points and all of the points between them. These given points are called the endpoints of the line segment. • Denoted by the two endpoints and a bar over the top or a lower case cursive letter. • Can be measured • Two line segments with the same measure are congruent. AB

6. Ray • A subset of points of a line from a given point (called the endpoint) infinitely in one direction. • Denoted by the letter representing the endpoint and one other letter on the ray, with a  over the two letters. AB

7. Angle • The union of 2 rays with a shared endpoint. The shared endpoint is called the vertex of the angle. • Can be denoted by an angle symbol and the letter denoting the vertex point (A) or in more complex figures by the angle symbol and three letters denoting a point on one ray, the vertex, and a point on the other ray (ABC)

8. Measuring an angle with a protractor • One ray is designated the initial ray and the other ray is designated the terminal ray. • When measuring rays with a protractor, the initial ray is line up with the bottom of the protractor, the vertex is lined up with the center of the protractor, and the terminal ray determines the angle’s measure. • Let’s practice using worksheet # __

9. Angle classification • Angles can be classified by their measures • Zero angle has measure zero degrees • Acute angles have measures between 0 and 90 degrees • Right or perpendicular angles have measures of exactly 90 degrees • Obtuse angles have measures between 90 and 180 degrees.

10. Angle classification • Straight angles have a measure of exactly 180 degrees and look like a line. • Reflex angles have a measure between 180 and 360 degrees. • Complementary angles are two angles whose measures have a sum of 90 degrees. • Supplementary angles are two angles whose measures have a sum of 180 degrees.

11. More practice • Go back to your worksheet and classify each angle based on the definitions just given. • In addition, on the back of the worksheet draw an example of a zero angle, a straight angle, a right angle, two complementary angles, and two supplementary angles.

12. A few more terms • Adjacent angles are angles that share a side. • Vertical angles are formed by the intersection of two lines. They share only the vertex. 1 4 2 3