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The Sum of the Interior Angles of a Triangle Equals 180 Degrees by Paper Folding

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midsegment and fold lines
Find the midpoints of
AB
and
AC
.
Connect the midpoints to form the midsegment.
Form the perpendicular folding lines to base
BC
.
folding controls
A
B
C
In high school geometry, various manipulatives (in class demonstrations, etc.) are used to show that the sum of the interior angles of a triangle equals 180 degrees. One simple example is to have the students cut off the three angles of a paper triangle and then rearrange these so that they all share a common vertex. The result is a visual proof that the sum is 180 degrees.
This Demonstration uses paper folding to show the result.
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