What is the measure of arc CD?

In the diagram above, line OA is congruent to line OB.

What is the measure of arc CD?
A . 27.5º
B . 55º
C . 70º
D . 110º
E . 125º

Answer: C

Explanation:

Triangle AOB is isosceles because line OA is congruent to line OB.

and

are both

55º, which means that

= 180 C (55 + 55) = 70º.

is a

central angle and arc CD is its intercepted arc. A central angle and its

intercepted arc are equal in measure, so the measure of arc CD is 70º.