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I'm pretty certain this doesn't work with a regular octagon (fully symmetric and equally long sides L). I suspect your solution works only if the diagonal sides in your picture have length sgrt(2)*L...

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You're wellcome.

I know it's an exercise but note that representing an octagon with 16 right triangles is very inefficient. All it takes are two points, the centre point and one perimeter corner...

It's easier with a picture but I'll try in words.

To get an octagon you inscribe a circle with 8 isosceles triangles. The angle between the equal sides of the triangles will be 45 degrees (8 time...