1. Perpendiculars and Distance
Distance between a point and a line – The distance from a line to a point not on the line is the length of the segment perpendicular to the line from the point.
Equidistant – A term indicating that the distance between two lines measured along a perpendicular line to the lines is always the same.

2. Perpendiculars and Distance
Distance between parallel lines – The distance between parallel lines is the length of the perpendicular segment with endpoints that lie on each of the two lines.
Theorem 3.9
In a plane, if two lines are equidistant from a third line, then the two lines are parallel to each other.

3. Draw the segment that represents the distance from
Answer:
Example 6-1b

4. Find the distance between the parallel lines a and b whose equations are and respectively.
Answer:
Example 6-3f