/sci/ - Science & Math

>>14642033
>>14642040
Mark out the centre of the octagon. Choose a side, and draw lines connecting the centre with both vertices. That's an isosceles triangle and the small angle is 45 degrees. 45 being a common angle means you can then use the cosine or sine rule to compute the other two sides, both of which equal the radius, and multiply by 2pi for the circumference.
That's how I'd solve it today and how I'd probably have solved it when I was twelve.
But I'd need to look up the cosine rule from somewhere because I don't really remember it off the top of my head.