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

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Postulate 3

Postulate 3: Intersection of Two Lines

If two lines intersect, then their intersection is a point.

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s

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Postulate 4

• Postulate 4: Intersection of Two Planes

• If two planes intersect, then their intersection is a line.

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.

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n

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

ED

C

F

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

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

SR

TU V

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.