Triangle Inequality Theorem Side Lengths Activity

Product description

From the author

This resource was created to PARTIALLY meet the requirements for the 7th Grade Math Geometry Standard below:

Ccss.math.content.7.g.a.2

Draw (freehand, with ruler and protractor, and with technology) geometric shapes with given conditions. Focus on constructing triangles from three measures of angles or sides, noticing when the conditions determine a unique triangle, more than one triangle, or no triangle.

In the classroom

Teaching tips & learning objectives

Learning objectives

Predict, then physically test with cut paper strips, whether three given side lengths can form a triangle
State the triangle inequality rule: the two shorter sides must sum to more than the longest side
Apply the inequality a + b > c to determine whether a new set of three side lengths forms a triangle

Teaching tips

Cut and, if reusing the set in future years, laminate the side-length strips ahead of time so groups can start testing right away
Put students in groups of 2-3, give each group one set of strips and one worksheet, and reserve the last 5-10 minutes of class for groups to share what they discovered
Show the page-4 example (strip ends must exactly touch to count as a triangle) before groups start testing, so they know what a valid match looks like

Skills covered

Triangle inequality reasoning — students test twelve side-length sets by hand, then generalize the rule that the two shorter sides must sum to more than the longest.
Inequality application — students use a + b > c to check six new side-length sets given in centimeters, inches, feet, millimeters, and yards.
Empirical mathematical discovery — students record a prediction, physically test it with the paper strips, and compare the result to what they predicted.

Good to know

Questions teachers ask about this resource

Do later triangle problems use the same measurement unit as the paper strips?

The hands-on strips are all in inches, but the six practice problems on the rule page switch to centimeters, feet, millimeters, and yards, so students apply the same rule across different units.

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Curriculum

Standards, concepts & topics

Standards

7.G.A.2

Core concepts

Triangle inequality theorem
Side lengths
Inequalities

Topics

Triangles Hands-on Triangle inequality theorem Triangle inequality rule Lengths of a triangle rule Triangle inequality theorem answer key

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Categories this resource belongs to

Math Activities Geometry Activities 7th Grade Activities Middle School Activities Activities Activities By Subject

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