It depends on what else is known about the sector: length of arc, area or some other measure.
if given the central angle and the area of the circle, then by proportion: Given angle / sector area = 360 / Entire area, then solve for the sector area
Find the area of the shaded sector. radius of 3 ...A+ = 7.07
If the sector of a circle has a central angle of 50 and an area of 605 cm2, the radius is: 37.24 cm
The area of the sector is: 221.2 cm2
Area of a sector of a circle = (pi) x (radius)2 x (central angle of the sector / 360)
(pi * radius squared) * ( sector angle / 360 )