We know that when the hours hands complete one full rotation it completes 12 hours or 360∘
Hence, we can say that,
⇒12hr=360∘
∴1hr=30∘
(a) Since from 9 to 12, there are 3 hours. Thus, to complete these 3 hours, hour hand has to move a particular angle which will give us the angle between the hour hand and the minute hand.
∴3hr=3×30∘=90∘
Thus, angle between the hands is 90∘
(b) There is 1 hour between the hands of the clock. Therefore, the required angles is,
⇒1hr=30∘
(c) There are 6 hours between the hands of the clock. Therefore, the required angles is,
⇒6hr=6×30∘=180∘