Section 3-1 Definitions

Two lines that do not intersect are either parallel or skew.

Coplanar lines that do not intersect Parallel Lines: lines Coplanar lines that do not intersect Known as Def’n of Lines

Segments and Rays contained in parallel lines are also considered parallel.

Skew Lines Noncoplanar lines that are neither parallel nor intersecting.

All planes are either parallel or intersecting!

Planes that do not intersect Parallel Planes Planes that do not intersect Known as Def’n of Planes For Example:

A line parallel to a plane The line and the plane will never intersect.

Theorem: If two parallel planes are cut by a third plane, then the lines of intersection are parallel.

A line that intersects two or more coplanar lines in different points. Transversal A line that intersects two or more coplanar lines in different points. Forms special types of angles a b l

Special Types of Angles: Alternate Interior Angles: two nonadjacent interior angles on opposite sides of the transversal Alternate Exterior Angles: two nonadjacent exterior angles on opposite sides of the transversal Consecutive Interior Angles: two interior angles on the same side of the transversal Corresponding Angles: two angles in corresponding positions relative to the two lines