# Angles of a Triangle: Triangles in the Trees

This is one lesson in a larger Unit Plan that covers many properties of triangles and several other theorems.  It has proofs, real world problems, constructions, a unit project, assessments, and more.  In Lesson 9, “Triangles in the Trees (Angles of a Triangle)”, students investigate the Triangle Sum Theorem, Triangle Inequality Theorem, and Exterior Angle Theorem.  One of the activities is a hands-on activity. Includes lesson plan, and a variety of downloadable student handouts (with and without Geometer's Sketchpad instructions).  The entire unit plan can be found here. The Lesson investigates Triangle Sum Theorem with a hands-on activity. The Triangle Inequality Theorem is discovered through a drawing activity, as is Exterior Angle Theorem. There are also several real world connections.

### Standards & Objectives

CLE 3108.4.1
Develop the structures of geometry, such as lines, angles, planes, and planar figures, and explore their properties and relationships.
CLE 3108.4.2
Describe the properties of regular polygons, including comparative classification of them and special points and segments.
GLE 0606.4.1
Understand and use basic properties of triangles, quadrilaterals, and other polygons.

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Learning objectives:

Essential Questions:

• What properties of sides and angles of triangles are used in everyday situations?
• Why should we study Triangle Sum Theorem, Triangle Inequality Theorem and Exterior Angle Theorem for Triangles?

### Lesson Variations

Blooms taxonomy level:
Understanding