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Chapter 1: Basics of Geometry

Difficulty Level: At Grade Created by: CK-12
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In this chapter, students will learn about the building blocks of geometry. We will start with the basics: point, line and plane and build upon those terms. From here, students will learn about segments, midpoints, angles, bisectors, angle relationships, and how to classify polygons.

Chapter Outline

Chapter Summary


This chapter begins with the basic components of Euclidean Geometry. From the introductory definition of points, lines, and planes it builds to a discussion of classifying figures such as angles, triangles, and polygons. Measurement of distances and angles are also covered. Different types of angle relationships are compared and explored, such as complementary angles, supplementary angles and linear pairs.

Symbol Toolbox for Chapter

Line, ray, line segment

Angle with vertex

Distance between and

Measure of




Chapter Keywords

  • Geometry
  • Point
  • Line
  • Plane
  • Space
  • Collinear
  • Coplanar
  • Endpoint:
  • Line Segment
  • Ray
  • Intersection
  • Postulates
  • Theorem
  • Distance
  • Measure
  • Ruler Postulate
  • Segment Addition Postulate
  • Angle
  • Vertex
  • Sides
  • Protractor Postulate
  • Straight Angle
  • Right Angle
  • Acute Angles
  • Obtuse Angles
  • Perpendicular
  • Construction
  • Compass
  • Angle Addition Postulate
  • Congruent
  • Midpoint
  • Midpoint Postulate
  • Segment Bisector
  • Perpendicular Bisector
  • Perpendicular Bisector Postulate
  • Angle Bisector
  • Angle Bisector Postulate
  • Complementary
  • Supplementary
  • Adjacent Angles
  • Linear Pair
  • Linear Pair Postulate
  • Vertical Angles
  • Vertical Angles Theorem
  • Triangle
  • Right Triangle
  • Obtuse Triangle
  • Acute Triangle
  • Equiangular Triangle
  • Scalene Triangle
  • Isosceles Triangle
  • Equilateral Triangle
  • Polygon
  • Diagonals

Chapter Review

Match the definition or description with the correct word.

Definition/Description Answer
1. When three points lie on the same line. A. Measure
2. All vertical angles are ________. B. Congruent
3. Linear pairs add up to _______. C. Angle Bisectors
4. The in from of . D. Ray
5. What you use to measure an angle. E. Collinear
6. When two sides of a triangle are congruent. F. Perpendicular.
7. G. Line
8. A line that passes through the midpoint of another line. H. Protractor
9. An angle that is greater than . I. Segment Addition Postulate.
10. The intersection of two planes is a ___________. J. Obtuse
11. K. Point
12. An exact location in space. L.
13. A sunbeam, for example M. Isosceles
14. Every angle has exactly one. N. Pentagon
15. A closed figure with 5 sides. O. Hexagon
P. Bisector

Texas Instruments Resources

In the CK-12 Texas Instruments Geometry FlexBook, there are graphing calculator activities designed to supplement the objectives for some of the lessons in this chapter. See http://www.ck12.org/flexr/chapter/9686.

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Difficulty Level:
At Grade
Date Created:
Jul 17, 2012
Last Modified:
Jan 14, 2016
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