Middle School Geometry--Grade 7--Lesson 4: Constructing Triangles

In this lesson, students learn how to construct triangles using only a compass and straightedge, focusing on equilateral, isosceles, scalene, and right triangles. They explore the conditions under which a triangle can be uniquely constructed from given side lengths or angles, and when construction is not possible. Aligned to CCSS.MATH.CONTENT.7.G.A.2, this lesson supports precise geometric reasoning and introduces students to foundational tools of geometric construction.

The lesson includes detailed, step-by-step examples that guide students through each type of triangle construction, along with embedded animated clip art that visually models the geometric processes. Special attention is given to cases involving the triangle inequality theorem and how reversing arc construction results in mirror-image triangles. Students also practice using protractors, compasses, and straightedges to construct triangles based on angle measures or side conditions.

This lesson includes a warm-up, vocabulary support, worked-out examples, a review section with advanced reasoning tasks, a 10-question quiz, and answer key. It also integrates links to Media4Math animated GIFs and geometry vocabulary resources, reinforcing visual learning and retention.

Subscribers to Media4Math can download the complete lesson plan in PDF format. This includes links to animations, vocabulary support, worked-out examples, a student quiz, and answer key.