# Introduction to Proportions

Click on the image at right to get the lesson app with instructor notes. Or you can install right from here by clicking the logo below: In this lesson app, students learn that a proportion is a statement that two ratios are equivalent, or equal. They also learn three different ways to identify a proportion from an equivalent ratio statement: divide the numerator and denominator of each ratio, divide across numerators and denominators, and cross multiply. Students explore proportions in the context of measuring heights and shadow lengths.

Another way students learn to identify a proportional relationship is using a graph. If two ratios form a proportion, then the points representing the ratios can be connected by a straight line that runs through the origin at (0, 0) on the coordinate plane. Students will plot ordered pairs given situations and then discern whether the relationship is proportional.

In the final module, students will learn that two angles whose measures have a sum of 90 degrees are called complementary angles, and two angles whose measures have a sum of 180 degrees are called supplementary angles. Students will use knowledge about this relationship, and some algebra from their previous years, to determine the degree measures of unknown angles.

Module 1 Video

This video shows how height is proportional to shadow length. It demonstrates that when two ratios are equal, they form a proportion. Knowing that a relationship is proportional can help you solve problems.