3-1 Lines and Angles
Parallel and Skew Parallel lines are coplanar lines that do not intersect. – The symbol means “is parallel to”. Skew lines are noncoplanar; they are not parallel and do not intersect. Parallel planes are planes that do not intersect. – A line and a plane can be parallel; segments and rays can be parallel or skew.
Identifying Nonintersecting Lines and Planes Which segments are parallel to AB? Which segments are skew to CD? What are two pairs of parallel planes? What are two segments parallel to plane BCGF? Why are FE and CD not skew?
Angles Pairs Formed by Transversals A transversal is a line that intersects two or more coplanar lines at different points (line t). Two angles are corresponding angles if they occupy corresponding positions (1 and 5, 3 and 7, 2 and 6, 4 and 8). Two angles are alternate exterior angles if they lie outside the two lines on opposite sides of the transversal (1 and 8, 2 and 7). Two angles are alternate interior angles if they lie between the two lines on opposite sides of the transversal (3 and 6, 4 and 5). Two angles are consecutive (or same side) interior angles if they lie between the two lines on the same side of the transversal (3 and 5, 4 and 6). tt
Identifying an Angle Pair Identify all pairs of angles with the following relationships: – Alternate interior – Same-side interior – Corresponding – Alternate exterior