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Homework Help: Area of Octagon

  1. Apr 13, 2004 #1
    I forgot the equation on how to solve for the area of an octagon. No information is given except that the total perimeter is 72 inches since we know that each side is 9-inch long.

    I looked up some stuff on the internet but it said we had to know the area from the middle of the shape to the outer edge (radius) in which I don't.

    Edit: Not sure, but I think the answer is somewhere around 390.96 inches squared?
    Last edited: Apr 13, 2004
  2. jcsd
  3. Apr 13, 2004 #2


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    You can break it up into triangles. If all of the interior angles and all sides are congruent, then you can think of it as a square with missing corners. The missing corners are 45-45-90 triangles.
  4. Apr 13, 2004 #3
    I seperated the Octagon into triangled. Then, I chose a triangle and cut it in half turning it into a 90 degree triangle (I have the measurement of 2 of the angles now).

    I knew what the base was (half of 9), then I used Tan to find the side of the height.

    After I did that, I found the area of the triangle and multiplied it by 8.
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