Geometry Vocabulary and Diagrams
A free Geometry lesson from the “Geometry Foundations” unit, with a worked example and practice problems including step-by-step solutions.
Geometry starts with precise language. Points mark locations, lines extend forever, segments have endpoints, rays extend in one direction, and planes are flat surfaces that extend forever.
What you'll learn
- Name basic geometry objects
- Read diagrams carefully
- Use notation accurately
Worked example
Problem. A segment has endpoints A and B. How should it be named?
- A segment is named by its endpoints.
- The order does not change the segment.
- It can be named segment AB or segment BA.
Answer: segment AB
Practice problems
1. Which object extends forever in both directions?
Choices: Line · Segment · Ray · Point
Show solution
- Warm-up: First identify exactly what the question is asking: Which object extends forever in both directions?
- Compare each answer choice with the calculation or rule, and eliminate choices that do not satisfy the condition.
- A line has no endpoints.
- Verify the selected choice by checking that it satisfies the original prompt and that the other choices fail the same test.
Answer: Line
2. Which object has two endpoints?
Choices: Segment · Line · Plane · Ray
Show solution
- Warm-up: First identify exactly what the question is asking: Which object has two endpoints?
- Compare each answer choice with the calculation or rule, and eliminate choices that do not satisfy the condition.
- A segment is finite.
- Verify the selected choice by checking that it satisfies the original prompt and that the other choices fail the same test.
Answer: Segment
3. A ray has...
Choices: One endpoint · Two endpoints · No endpoints · Only area
Show solution
- Core Practice: First identify exactly what the question is asking: A ray has...
- Compare each answer choice with the calculation or rule, and eliminate choices that do not satisfy the condition.
- A ray starts at one point and extends in one direction.
- Verify the selected choice by checking that it satisfies the original prompt and that the other choices fail the same test.
Answer: One endpoint
4. How many degrees are in a right angle?
Show solution
- Core Practice: First identify exactly what the question is asking: How many degrees are in a right angle?
- Use the relevant geometric relationship first, then set up an equation from the angle measures or side relationships.
- A right angle measures 90 degrees.
- Check the result by substituting or estimating: the response should match 90 and make sense in the original problem.
Answer: 90
5. Two lines in the same plane that never meet are...
Choices: Parallel · Perpendicular · Congruent · Collinear
Show solution
- Core Practice: First identify exactly what the question is asking: Two lines in the same plane that never meet are...
- Compare each answer choice with the calculation or rule, and eliminate choices that do not satisfy the condition.
- Parallel lines do not intersect.
- Verify the selected choice by checking that it satisfies the original prompt and that the other choices fail the same test.
Answer: Parallel
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