4. Perimeter and Area in the Coordinate Plane
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Concave quadrilateral
The polygon has four sides which makes it a quadrilateral.A polygon is concave if a line that contains a side of the polygon contains a point in the interior of the polygon. Let's draw such a line containing Side 3.
It is possible to draw a line along this side of the polygon and make it cross the interior, so the polygon is concave.