## Overview

**Learning Intentions (Objectives)**

- Students will use angle properties to classify triangles and find congruent angles.
- Students will explore the Triangle Sum Theorem and use it to find unknown angle measures.

### Lesson Components

- Explore
- Try This! (Classifying Triangles)
- Try This! (Sums of Triangle Interior Angles)
- Watch (Triangle Sum Theorem)
- Try This! (Congruent Angles)
- Practice

### Content Standards Addressed in the Lesson

**4.G.1.** Draw points, lines, line segments, rays, angles (right, acute, obtuse), and perpendicular and parallel lines. Identify these in two-dimensional figures.

**4.G.2.** Classify two-dimensional figures based on the presence or absence of parallel or perpendicular lines, or the presence or absence of angles of a specified size. Recognize right triangles as a category, and identify right triangles. (Two-dimensional shapes should include special triangles, e.g., equilateral, isosceles, scalene, and special quadrilaterals, e.g., rhombus, square, rectangle, parallelogram, trapezoid.) CA

**HSG.CO.C.10.** Prove theorems about triangles. Theorems include: measures of interior angles of a triangle sum to 180°; base angles of isosceles triangles are congruent; the segment joining midpoints of two sides of a triangle is parallel to the third side and half the length; the medians of a triangle meet at a point.