We denote this angle by the same symbol as the vertex. The area of a polygon whose vertices have coordinates , for , is the absolute value of where in the sumation we take and . In oblique coordinates with angle between the axes, the area is as given above, times sin . If the vertices have polar coordinates , for , the area is the absolute value of where we take and . Formulas for specific polygons in terms of side lengths, angles, etc. are given in the next sections.
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