# 180° In a Triangle Experiment

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Follow the instructions below to show that there are 180° in a triangle.

 1. Cut out the triangle as close to the lines as possible. 2. Cut or carefully tear the triangle into three similar sizes as shown above. 3. Line up the pieces along a straight line with the three vertices touching.

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Follow the instructions below to show that there are 180° in a triangle.

 1. Cut out the triangle as close to the lines as possible. 2. Cut or carefully tear the triangle into three similar sizes as shown above. 3. Line up the pieces along a straight line with the three vertices touching.

You will find a related lesson on finding missing angles here. There is also a similar activity in this how many degrees in a quadrilateral worksheet.

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### Related Resources

The various resources listed below are aligned to the same standard, (8G05) taken from the CCSM (Common Core Standards For Mathematics) as the Geometry Worksheet shown above.

Use informal arguments to establish facts about the angle sum and exterior angle of triangles, about 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.

#### Worksheet

Similar to the above listing, the resources below are aligned to related standards in the Common Core For Mathematics that together support the following learning outcome:

Understand congruence and similarity using physical models, transparencies, or geometry software

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