In circle o, ac and bd are diameters.

what is m(arc)ab? 72° 108° 120° 144°

72°
108°
120°
144°

 The correct option is (C) 120°.

Step-by-step explanation:  Given that Ac and BD are the diameters of the circle with center 'O'.

We are to find the measure of arc AB.

Since AC and BD are diameters of the circle, and diameters subtends an angle of 180° at the center, so we have

From the figure, we get

Since the diameters AC and BD intersect at the center 'O', so ∠AOC and ∠BOD are vertically opposite angles. Hence, they must be equal.

So,

Therefore, from equation (i), we get

Thus, the measure of arc AB is 120°. Option (C) is correct.