Circular arc--badly stuck I have a circular arc defined by 3 points [start point, intermediate point an end point]. I know the radius of the circular arc too. I know the angle subtended by the start and end point at the centre. I do not know the center of the circle Now, I want to calculate the length of the arc using s = r * theta "r" being the radius and "theta" the angle subtended by the start and end point at the centre.[theta being the smaller included angle] Now, i get a length "L" But in some problems my answer is correct value "L" but in some cases the answer i need is 2*pi - L [that corresponding to bigger included angle] but i get "L".This i checked graphically-- Howm to get the correct validation algebraically?