Since there are 360 degrees in a circle, we have 360/90=4, meaning that sector AOB is 1/4th of the area of the circle. Since the area of a circle is πr², we can plug that in to get 3.14(2.5)²=19.625 as our total area. Since AOB is 1/4 of that, we multiply 19.625 by 1/4 to get 4.90625 as the area of sector AOB
