Why does a circles angles equal up to 2pi? Wouldn't it be 1pi? Please help. My geometry teacher (last year - and now he's gone) drew a circle for me and defined all the points in terms of pi (is there an ASCII character for pi, by-the-way, on the keyboard?). Where the 90 degree point would be he put 1/2 pi, were the 180 degree point was he put just 'pi', at 270 he put 3/2 pi, and 360 he put 2 pi. What the heck?! I thought pi was the ratio of the diameter to the circumference. If that is true then shouldn't it be: at 90 degrees 1/4 pi, at 180 deg. 1/2 pi, 270 deg. 3/4 pi, and 360 deg. just 'pi'? Can you explain this or direct me to a site that can? Please, I'm going crazy trying to figure it out.