A line that has one defined endpoint is called a ray and extends
endlessly in one direction. A ray is named after the endpoint and
another point on the ray e.g.
The angle that is formed between two rays with the same endpoint
is measured in degrees. The point is called the vertex
The vertex is written as
In algebra we used the coordinate plane to graph and solve
equations. You can plot lines, line segments, rays and angles
in a coordinate plane.
In the coordinate plane above we have two rays
That form an angle with the vertex in point B.
You can use the coordinate plane to measure the length of a line
segment. Point B is at (-2, -2) and C (1. -2). The distance between
the two points is 1 - (-2) = 3 units.
Angles can be either straight, right, acute or obtuse.
An angle is a fraction of a circle where the whole circle is
360°. A straight angle is the same as half the circle and is 180°
whereas a right angle is a quarter of a circle and is 90°.
You measure the size of an angle with a protractor.
Two angles with the same measure are called congruent angles.
Congruent angles are denoted as
Or could be shown by an arc on the figure to indicate which
angles that are congruent.
Two angles whose measures together are 180° are called
supplementary e.g. two right angles are supplementary since 90° +
90° = 180°.
Two angles whose measures together are 90° are called
complementary.
Video lesson: Measure the size of the angle