<PRE><B>Question 1101442</B>
if the vertices of a triangle are A (1,3) B (3,4) and C (1,-4) find its area. 
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Here&#39;s another method.
&lt;pre&gt;
 A   B   C   A
 1   3   1   1
 3   4  -4   3
&lt;/pre&gt;
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Add the diagonal products starting at the upper left.
4 -12 + 3 = -5
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Add the diagonal products starting at the lower left.
9 +4 -4 = 9
The difference is 14
The area is 1/2 that,
Area = 7 sq units
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This methods works for ALL polygons, any number of sides.
The points must be in order around the polygon.

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