Find the central angle θ which forms a sector of area 21 square feet of a circle of radius 11 feet.
Solution:-
A central angle is an angle whose vertex is at the center of a circle. The rays of a central angle subtend (intersect) an arc on the circle. The part of the circle between the rays of the angle and the arc subtended is called a sector.
Area of a sector
The area A of sector of a circle of radius r formed by a central angle of θ radians is equal to the following
A = 
r2 θ
Solving for θ given θ = 
.
Substitute the values for A and r, and simplify.
θ =
=
0.347
Therefore, the central angle θ which forms a sector of area 21 square feet of a circle of radius 11 feet is θ = 0.347 radians.