3-1 Lines and Angles
Types of lines
1)Intersecting—share at least one point. If they share more than one point, then the lines
are the same line. Intersecting lines are in the same plane
Special intersecting lines: Perpendicular—intersect at 90° (right) angles.
c  e Notice the  mark. This is how to write perpendicular
2) parallel. Parallel lines are coplanar, never intersect and are always the equidistant (same)
distance apart. They are in the same plane
p || q Notice the || marks. This is how to write it
We mark parallel lines with arrows someplace on the lines
3) Skew lines—non-intersecting, non-parallel lines. Skew lines are in different planes
Two planes can
1. Intersect. The intersection of two planes is a line
2. Not intersect. The planes are parallel
A || B
Transversal—a line that intersects two coplanar lines at two different points.
Corresponding angles—lie on the same side of the transversal, on the same sides of the lines
Pairs of Corresponding angles
< 1 and < 5
< 3 and < 7
< 2 and < 6
< 4 and < 8
Alternate Interior Angles—are nonadjacent angles that lie on opposite sides of the transversal,
between the lines
Alternate Interior angles
< 3 and < 6
< 4 and < 5
Alternate Exterior Angles—lie on opposite sides of the transversal, outside the lines. In the
above diagram, < 2 and < 7 and < 1
and < 8 are two pairs of alternate exterior angles.