/line - линия; line segment - отсечка; ray - лъч; angle - ъгъл; /

When two rays share a point they form an angle.

## Slope §

A slope of a line is the change in coordinate () with respect to to the change in coordinate ().

To find the slope of and

If the slope of a line is zero, then the line is perfectly horizontal.

If the slope of a line is undefined, then the line is perfectly vertical.

If a line is perfectly vertical & another line is perfectly horizontal, then the lines are perpendicular to each other.

### Parallel lines §

If the slopes of two lines are equal, then they are parallel.

### Perpendicular lines §

If the slope of one line is the negative and reciprocal of the another line, then the two lines are perpendicular.

## Distance §

### In two-dimension §

The distance between two points in the second dimension can be found using:

### Midpoint §

The midpoint of a line segment is the point that is equidistant from both endpoints of the line segment. It bisects the segment.

To find the midpoint of a line segment , where and