You can put this solution on YOUR website! Let's look at a regular decagon.
Draw it out, it doesn't have to be perfect.
You have 10 sides and 11 vertices where the sides intersect.
Find the center of the decagon and draw lines from the vertices to the center point.
You'll get 10 identical isoceles triangles shown here with angles A,B, and B.
Only three of the ten triangles are shown here for simplicity.
From the rules for triangles, you know that
1.
1.
You also know from the diagram that
2.
2.
since the sum of the A angles equals one revolution and there are 10 A angles(10 triangles total).
The interior angle of a regular decagon is 2B.
From 1,
1.
1.
1.
The interior angle of a regular decagon is 144 degrees.
