



 
Richard, I joined the opposite vertices to subdivide the octagon into 8 triangles which all have a common vertex at the centre C of the octagon. The measure of the angle BCA is then 360^{o}/8 = 45^{o}. Triangle BCA is an isosceles triangle and hence angles ABC and CAB have the same measure (180^{o}  45^{o})/2 = 67.5^{o}. This is the angle of the cut. To calculate the side lengths I added to the diagram. Suppose each side is x feet long. Triangle APQ is a right triangle so Pythagoras theorem tells us that the length of PQ is feet. Hence . Thus
which is 2 feet 5 ^{13}/_{16} inches. I hope this helps,  


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