# A stop sign has the shape of a regular octagon. What is the sum of the interior angles of a stop sign?

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The sum of the interior angles can be calculated easily by understanding where the formula comes from.

For an octagon: Sum =

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In any polygon, you can divide it up into triangles by joining one vertex to all of the others. You will find that the number of triangles is ALWAYS 2 less than the number of sides.

ie 3 sides gives 1 triangle. 6 sides gives 4 triangles, 10 sides gives 8 triangles and so on..

But, the sum of the angles in any triangle is always 180°.

So, subtract 2 from the number of sides and multiply by 180°.

This is exactly what

An octagon has 8 sides, which means

So the sum of the interior angles is:

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Describe your changes (optional) 200

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Use the interior sum formula ..

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Sum

hope that helped

Describe your changes (optional) 200