Question

AC is a diameter of D. If m BDC = 45°, what is the measure of AB?

45°
135°
180°
155°

(I think it's either B or D)

Answer 1

To find out what ADB equals you need to subract 45 from 180. 
After you do that it should equal 135 degrees. 
So the answer is B.

Answer 2

Answer:

135°

Step-by-step explanation:

The AC line is the diameter of the circle, and it is a straight line so the angle AC measures 180 °.

The image tells us that the angle BDC measures 45 °, so to find the angle AB we must subtract to the measure of the angle AC the measure of the BDC: agulo:

AC - BDC = 180 ° - 45 ° = 135 °