(a). The angle AOD is 62 degrees.
(b). The angle ABC is 31 degrees.
(a). From given diagram, It is observed that triangle AOD is a right angle triangle.
The sum of all three angles in triangle is equal to 180 degrees.
[tex]\angle A +\angle O + \angle D = 180\\\\90 +\angle AOD +28=180\\\\\angle AOD=180-90-28=62[/tex]
(b). The central angle theorem states that the angle subtended by an arc at the center of the circle is double the angle subtended at any point on the circumference of the circle.
[tex]\angle ABC = \frac{1}{2} \angle AOD\\ \\\angle ABC=\frac{1}{2}*62=31[/tex]
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