If 20 m of wire is available for fencing off a flower-bed
Question: If 20 m of wire is available for fencing off a flower-bed in the form of a circular sector, then the maximum area(In sq m) of the flower bed is
(a) 12.5Â Â Â Â Â Â Â Â Â Â Â Â (b) 10
(c) 25Â Â Â Â Â Â Â Â Â Â Â Â Â Â (d) 30
Solution:- The correct option is (C)
Let the radius of circular sector = rÂ
Angle made by sector in centre
Total length
Now area of flower bed
differentiate with respect to r
For max and minima,
Again differerntiate with respect to r
Hence, the area is max when
Max area
sq.m
The correct option is (C)