These free geometry worksheets will introduce you to the Exterior Angle Sum Theorem, as you find the measurements of the exterior angles of a triangle.  The exterior, or outside, angles of a triangle are always congruent to the two non-adjacent, interior angles of the triangle.  In plain English, the outside angles is equal to sum of the two inside angles that are farthest away.

Like most of the worksheets at www.imathworksheets.com, this is a progressive series.  That means we start with the easy problems and add a new twist to each successive worksheet.  Of course, answer keys are provided as well.

Exterior Angles of a Triangle Worksheet 1 - This angle worksheet features 12 different triangles, all with one clearly identified exterior angle, represented by x.  The measurements of the three interior angles are given.  Simply add the two non-adjacent angles, and you have found the measure of the exterior angle.

Exterior Angles of a Triangle Worksheet 1 RTF
ExteriorAngles of a Triangle Worksheet 1 PDF
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Exterior Angles of a Triangle Worksheet 2 - This angle worksheet features 12 different triangles, all with one or more exterior angle.  Some additional angle measures are given to make sure you can identify the angles that you need, the two non-adjacent angles.

Exterior Angles of a Triangle Worksheet 2 RTF
ExteriorAngles of a Triangle Worksheet 2 PDF
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Exterior Angles of a Triangle Worksheet 3 - You’ll need to use all of your knowledge about exterior and interior angles for this 12 problem angle worksheet.  Sometimes you’ll  need to use the exterior angle to find the interior angle, and vice-versa.  Fortunately, no algebraic expressions are thrown in, yet.

Exterior Angles of a Triangle Worksheet 3 RTF
ExteriorAngles of a Triangle Worksheet 3 PDF
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Exterior Angles of a Triangle Worksheet 4 - This 12 problem angle worksheet represents the missing angles with algebraic expressions like 3x and 7x – 4.  You’ll need to use your knowledge of exterior angles to set up equations and solve for x.  Then, you’ll have to plug your solution into each expression to find the missing angles.

Exterior Angles of a Triangle Worksheet 4 RTF
ExteriorAngles of a Triangle Worksheet 4 PDF
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