Question 1101896
Given A (-3,2), B (2,7) and C (8,10), find the area of the triangle ABC.
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<pre>
 A   B   C   A
-3   2   8  -3
 2   7  10   2
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</pre>
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Add the diagaonal products starting upper left.
-3*7 + 2*10 + 8*2 = 15
Add the diagaonal products starting lower left.
2*2 + 7*8 -3*10 = 30
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The difference is 15.
The area is 1/2 that = 7.5 sq units
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Works for all polygons, any # of sides.
The points have to be in order around the polygon.