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Re: weikehua@gmail.com
LensmireJohn - 2021年10月26日 Tuesday 11:24
 

Here's a hint: A regular octagon has interior angles of 135 degrees. Note that 180 - 135 = 45, so the external angles are 45 degrees. Therefore, adding 45-45-90 isosceles to four corners of an octagon can create a large square. Then the octagon's area can be found by taking the square's area and subtracting the four triangles.