1. 1.4 Intersections In geometry, figures intersect if they have any points in common. The intersection of two or more figures is the point or points that the figure have in common. A s t

2. Postulate 3 Postulate 3: Intersection of Two Lines If two lines intersect, then their intersection is a point. P s t

3. Postulate 4 Postulate 4: Intersection of Two Planes If two planes intersect, then their intersection is a line.

5. Visualize it! Two lines can intersect even if the diagram does not show where they intersect. The lines below intersect at a point that is not shown. m n

6. Example 1 Use the diagram at the right. a. Name the intersection of AC and BE. b. Name the intersection of BE and DF. c. Name the intersection of AC and DF. A B E D C F

7. Example 2 Use the diagram at the right. a. Name the intersection of planes S and R. b. Name the intersection of planes R and T. c. Name the intersections of planes T and S. S R T k l

8. Checkpoint Use the diagram at the right. 1. Name the intersection of PS and QR. 2. Name the intersection of TV and QU. 3. Name the intersection of PS and UV. P Q S R T U V

9. Checkpoint Use the diagram at the right. Name the intersection of planes Q and L. Name the intersection of planes Q and Z. Name the intersection of planes Z and L.