The formula for calculating side length, a, using the diameter, d, is a = d × sin α, where α is the isosceles triangles' apex angle.
The dimension of a standard letter in the US is 8.5 × 11 inches. So, we can cut a square of maximum length 8.5 × 8.5 inches. Hence, the octagon's maximum diameter, d, is 8.5 in. Thus, the side length = 8.5 in × sin 45 = 6 in.
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