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 Aug 29, 2018
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You see, the first one is a hexagon(6-gon), so the sum of interior angle is: 

\((6-2)\cdot(180^{\circ}) = 720^{\circ}\)

The second one is a pentagon(5-gon) although it is a concave pentagon. But in fact, you still use the same formula for this.

The sum of interior angle is:

\((5-2)\cdot(180^{\circ}) = 540^{\circ}\)

 

Edit:

Explanation for (n-2)*(180 degrees):

For any polygon, start from one of the vertices, then repeatedly draw an edge to another vertice, until all the vertices are directly connected with an edge. If the polygon is an n-gon, then it should now be divided into (n-2) triangles. So the sum of  interior angles should be (n-2)*(180 degrees).

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 Sep 1, 2018
edited by MaxWong  Sep 1, 2018

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