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# More on the Angles of Triangles (Exterior Angle Theorem) - 8.2 - Lesson 14

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Author: Todd Parks

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Tutorial

## Rules for Triangle Angles

We need to remember that ALL triangles (right triangles, obtuse triangles, and acute triangles), their interior angles ALWAYS add up to 180 degrees.

Also, two angles that are adjacent to each other (next to each other), that form a straight line, also add up to 180 degrees.  We see this when a side of a triangle is extended.  The interior angle and exterior angle add up to 180 degrees.

## Straight Angle Theorem

We already know our triangle angle theorem, which is the three interior angles of any triangle add up to 180 degrees.

Now we have our straight angle theorem which states that any straight line will also equal 180 degrees.

## Mr. Parks' Examples of Lesson 14

In the video, Mr. Parks goes over a couple of the examples in lesson 14 covering how to find exterior and interior angles of a triangle.

## IXL - Exterior Angle Theorem

Here is the IXL target that coordinates with exterior angles of triangles in lesson 14 of module 2.

Practice and discover before trying the quiz above.

http://www.ixl.com/math/geometry/exterior-angle-theorem

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