Two circles with same radius intersect, so that the outermost point of either circle goes through the other's center. Arc [tex]SPX[/tex] has length [tex](3/4)*\pi[/tex] (see attached image.) What is the radius of either circle? I think I could solve this problem if I knew the central angle SX, but I don't know how to identify when they hit (X). Maybe I have to form some special triangle into the image.