Find the value of c using the given chord and secant lengths in the diagram shown to the right c = (Round to the nearest tenth as needed.) Solution here we apply pythagoras theorem. The radius will touch the mid points of both the secants 1stly we have (10+10)^2 +r^2 =C^2 (c is the common line) and (13+c/2)^2 +r^2 =C^2, so using this we get -> 20=13+c/2 => c = 14.