Basic Technical Mathematics, 11th Edition

2.1 Lines Angles

• Basic Angles • Parallel Lines Perpendicular Lines • Supplementary Angles Complementary Angles • Angles Between Intersecting Lines • Segments of Transversals

It is not possible to define every term we use. In geometry, the meanings of point, line, plane are accepted without being defined. These terms give us a starting point for the definitions of other useful geometric terms.

The amount of rotation of a ray (or half-line) about its endpoint is called an angle. A ray is that part of a line (the word line means “straight line”) to one side of a fixed point on the line. The fixed point is the vertex of the angle. One complete rotation of a ray is an angle with a measure of 360 degrees, written as $360\hspace{0.17em}°\hspace{0.17em}\text{.}$ Some special types ...