1. Learn to describe figures by using the terms of geometry.

2. Vocabulary
point
line
plane
line segment
ray

3. The building blocks of geometry are points, lines, and planes.

4. Additional Example 1: Identifying Points, Lines, and Planes
Use the diagram to name the geometric figure.
A. three points
M, N, and P
Five points are labeled: points M, N, P, Q, and R.
B. two lines
PR and NR
You can also write RP and RN.

5. Additional Example 1: Identifying Points, Lines, and Planes
Use the diagram to name the geometric figure.
C. a point shared by two lines
point R
Point R is a point on PR and NR.
D. a plane
plane QRM
Use any three points in the plane that are not on the same line Write the three points in any order.

6. Use the diagram to name the geometric figure.
Check It Out: Example 1
Use the diagram to name the geometric figure.
A. three points
S, T, and U
Five points are labeled: points S, T, U, V, and W. V S U W T
B. two lines
UW and SW
You can also write WU and WS.

7. Use the diagram to name the geometric figure.
Check It Out: Example 1
Use the diagram to name the geometric figure.
C. a point shared by two lines
point W
Point W is a point on WS and WU. V S U W T
D. a plane
plane VUT
Use any three points in the plane that are not on the same line Write the three points in any order.

9. Additional Example 2: Identifying Line Segments and Rays
Use the diagram to give a possible name to the figure.
A. three different line segments C A B
AB, BC, and AC
You can also write BA, CB, and CA.
B. three ways to name the line
AB, BC, and AC
You can also write BA, CB, and CA.

10. Additional Example 2: Identifying Line Segments and Rays
Use the diagram to give a possible name to the figure.
C. six rays C A B
AB, AC, BC, CB,
CA, and BA
D. another name for ray AB AC
A is still the endpoint C is another point on the ray.

11. A. three different line segments
Check It Out: Example 2
Use the diagram to give a possible name to the figure.
A. three different line segments F D E
DE, EF, and DF
You can also write ED, FE, and FD.
B. three ways to name the line
DE, EF, and DF
You can also write ED, FE, and FD.

12. D. another name for ray DE
Check It Out: Example 2
Use the diagram to give a possible name to the figure.
C. six rays F D E
DE, EF, DF, FE,
FD, and ED
D. another name for ray DE DF
D is still the endpoint F is another point on the ray.

13. Lesson Quiz
Use the diagram to name each geometric figure.
1. three points
2. two lines
3. a point shared by a line and a ray
4. a plane
Possible answer: A, B, C
Possible answer: AD, CE
Possible answer: F
Possible answer: plane AEC