For the answer to the question above, the answer is 30 cm. CD and AB both intersect with each other creating a right angle. The radius is 17 so the line in red connecting point A and point C is 17 as that's a radius. Because the lines form a right triangle, you can use the Pythagorean theorem to solve for the missing length. so if CD is 16, half of that is 8. 17 squared minus 8 squared is 225. Find the square root which gives you 15. 15 is only HALF the length of AB so you'd have to basically repeat to the other side (which is basically a waste of time so just multiply 15 by 2) I hope this helps