Urgent: How do you find the lengths of sides for shapes inscribed within a circle of radius=1cm?

I am writing an essay on cyclogons..... and I am trying to find the respective lengths of sides for regular polygons: more specifically an equilateral triangle, square, regular pentagon, and regular hexagon. I have never studied this before and don't know how to determine what the sides need to be in length to be inscribed in the unit circle. Thanks in advanced!