Question 470192: Find the area of a rectangle with the vertices at (0,9) (0,-4) (5,-4) and (5,9)
Answer by Alan3354(69443)   (Show Source):
You can put this solution on YOUR website! Find the area of a rectangle with the vertices at (0,9) (0,-4) (5,-4) and (5,9)
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it's 5 by 13
Area = 65
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Here's a general solution:
Label the points in order:
A(0,9) B(0,-4) C(5,-4) and D(5,9)
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A B C D A
0 0 5 5 0
9-4-4 9 9
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Add the diagonal products from the upper left:
0 + 0 + 45 + 45 = 90
Add the diagonal products from the lower left:
0 - 20 - 20 + 0 = -40
The difference is 130
The area is 1/2 that = 65 sq units.
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It works for all polygons, any number of sides.
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