1. State which postulate justifies each statement.
1. If D is in the interior of ABC, then m ABD + m DBC = m ABC.
ANSWER
Angle Addition Postulate
2. If M is between X and Y, then XM + MY = XY.
ANSWER
Segment Addition Postulate

2. EXAMPLE 1
Identify a postulate illustrated by a diagram
State the postulate illustrated by the diagram. a. b.
SOLUTION a.
Postulate 7: If two lines intersect, then their intersection is exactly one point. b.
Postulate 11: If two planes intersect, then their
intersection is a line.

3. EXAMPLE 2
Identify postulates from a diagram
Use the diagram to write examples of Postulates 9 and 10.
Postulate 9: Plane P contains at
least three noncollinear points,
A, B, and C.
Postulate 10: Point A and point B lie in plane P,
so line n containing A and B also lies in plane P.

4. GUIDED PRACTICE
for Example 1 and 2
Use the diagram in Example 2 to write examples of Postulates 5, 6, and 7. 2.
ANSWER
Postulate 5 :
Line n passes through points A and B
Postulate 6 :
Line n contains A and B
Postulate 7 :
Line m and n intersect at point A

5. EXAMPLE 3
Use given information to sketch a diagram
Sketch a diagram showing TV intersecting PQ at point W, so that TW WV .
SOLUTION
STEP 1
Draw TV and label points T and V.
STEP 2
Draw point W at the midpoint of TV Mark the congruent segments.
STEP 3
Draw PQ through W.

6. EXAMPLE 4
Interpret a diagram in three dimensions
Which of the following statements cannot be assumed from the diagram?
A, B, and F are collinear.
E, B, and D are collinear.
AB plane S
CD plane T
AF intersects BC at point B.
SOLUTION
No drawn line connects E, B, and D, so you cannot assume they are collinear. With no right angle marked, you cannot assume CD plane T.

7. GUIDED PRACTICE
for Examples 3 and 4
In Questions 3 and 4, refer back to Example 3. 3.
If the given information stated PW and QW are congruent, how would you indicate that in the diagram?
ANSWER

8. GUIDED PRACTICE
for Examples 3 and 4 4.
Name a pair of supplementary angles in the
diagram. Explain.
ANSWER
In the diagram the angle TWP and VWP form a linear pair So, angle TWP, VWP are a pair of supplementary angles.

9. GUIDED PRACTICE
for Examples 3 and 4 5.
In the diagram for Example 4, can you assume
plane S intersects plane T at BC ?
ANSWER
Yes

10. GUIDED PRACTICE
for Examples 3 and 4 6.
Explain how you know that AB BC in Example 4.
ANSWER
It is given that line AB is perpendicular to plane S, therefore line AB is perpendicular to every line in the plane that intersect it at point B. So, AB BC

11. Daily Homework Quiz 1.
Use the diagram to write an example of Postulate 7.
ANSWER
Line m intersects line n in point F and no other point.

12. Daily Homework Quiz 2.
Decide whether the statement “Two planes can intersect in exactly one point R” is true or false. If false, give a reason.
ANSWER
False; Postulate 11 says that if two planes intersect, their intersection is a line.

13. Daily Homework Quiz
Use the diagram to determine if the statement is true or false. 3.
The intersection of planes M and N is points B, E and H.
ANSWER
false

14. Daily Homework Quiz
Use the diagram to determine if the statement is true or false. 4.
GH lies in plane M.
ANSWER
true

15. Daily Homework Quiz
Use the diagram to determine if the statement is true or false. 5.
ABE and HED are vertical angles.
ANSWER
false