Lesson 2.5 Angle Relationships Answer Key

Lesson 2.5 Angle Relationships Answer Key: Understanding Angles and Their Relationships

Angles are a fundamental aspect of geometry, and their understanding is essential for properly comprehending various geometric concepts and theorems. In lesson 2.5 angle relationships, students are introduced to angles and their properties; they learn to identify types of angles, measure their values, and explore their relationships. This article discusses the importance of lesson 2.5 angle relationships, its objectives, and provides an answer key for the exercises in it.

Importance of Lesson 2.5 Angle Relationships

Angle relationships form the basis of all geometric concepts, including area, similarity and congruence, and transformation. Understanding angles is an essential prerequisite for developing problem-solving skills and critical thinking abilities, which are crucial in various fields like engineering, architecture, and mathematics.

Learning how to identify angles and measure their values help students communicate mathematical ideas and concepts, increasing their proficiency in the language of mathematics. Moreover, students will learn how to apply geometrical principles to solve problems in various aspects of life, including construction, architecture, and engineering.

Objectives of Lesson 2.5 Angle Relationships

Lesson 2.5 angle relationships aim to teach students about angles, their types, and their relationships. The lesson has the following objectives:

  1. Identify the types of angles

Here, students learn about the different types of angles such as acute, right, obtuse, straight, and reflex angles. By understanding the angle types, students can easily identify each angle’s properties and relationships.

  1. Measure the value of angles

In this section of the lesson, students learn how to measure angles using the degrees measurement system. The degree measurement system is crucial in solving various types of geometry problems, and understanding it enables students to calculate angles accurately.

  1. Explore angle relationships

The students will learn about the relationships between angles, including adjacent, vertical, complementary, and supplementary angles. Students familiarize themselves with the ways angles interact and their sum value.

Answer Key for Lesson 2.5 Angle Relationships

The following is an answer key for the lesson 2.5 angle relationships exercises:

  1. Identify whether the angle is acute, obtuse, or right:

A. 70 degrees – Acute angle
B. 110 degrees – Obtuse angle
C. 90 degrees – Right angle
D. 30 degrees – Acute angle

  1. Calculate the sum of interior angles of a polygon with five sides.

The sum of interior angles for a polygon with n-sides is given by the formula: (n-2) x 180 degrees. Therefore, for a polygon with five sides: (5-2) x 180 degrees = 540 degrees.

  1. Identify the type of angle pair:

A. 65 degrees and 115 degrees – Supplementary angles
B. 40 degrees and 50 degrees – Complementary angles
C. 70 degrees and 70 degrees – Vertical angles
D. 115 degrees and 65 degrees – Supplementary angles


In conclusion, lesson 2.5 angle relationships is critical in introducing students to angles, their properties, and relationships. The lesson is fundamental in laying the foundation for more advanced geometry concepts, including similarity and congruence, and transformation. Understanding angle concepts and related problems enables students to foster problem-solving skills, enhances critical thinking abilities and promotes proficiency in the language of mathematics. This article includes an answer key that aids students in checking their progress and understanding of the lesson.

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