# 1.C: Proportions and Similar Polygons


## Overview

The purpose of this lesson is to use properties of similar polygons and proportions to find unknown measures.

This lesson will address the following CCRS Standard(s) for Geometry:

• 7.G.1: Solve problems involving scale drawings of geometric figures, including computing actual lengths and areas from a scale drawing and reproducing a scale drawing at a different scale
• 8.G.5: Use informal arguments to establish facts about the angle sum and exterior angles of triangles, above the angles created when parallel lines are cut by a transversal, and the angle-angle criterion for similarity of triangles. For example, arrange three copies of the same triangle so that the sum of the three angles appears to form a line, and give an argument in terms of transversals why this is so

## Directions

1. Take notes while watching videos below
2. Go to http://wamap.org and log into our course to complete assignment 1.C with 80% or better.

### Watch

Proportions and Similar Polygons [7:11]

### Do

Complete assignment 1.C with 80% or better at http://wamap.org

## Summary

In this lesson we have learned:

• Given the proportion , we can solve by multiplying diagonals to get ad = bc.
• If to polygons are similar, then corresponding sides are proportional
• If two angles of one triangle are congruent to two angles of another triangle, then the triangle's sides are proportional.

1.C: Proportions and Similar Polygons is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.