The given circles are concentric with centre at (0, 0) and the length of the perpendicular from (0, 0) on the given line is p. Let OL = p Then, AL = √(OA)2−(OL)2 = √a2−p2 And PL = √(OP)2−(OL2) = √b2−p2 ⇒ AP = √a2−p2−√b2−p2