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Question:

Twenty meters of wire is available for fencing off a flower-bed in the form of a circular sector. Then the maximum area (insq.m) of the flower-bed, is.

10

12.5

25

30

Solution:

20=2r+l
l=20-2r
A=1/2*lr
A=1/2(20-2r)r
dA/dr=1/2[20-4r]=0
4r=20
r=5
A=1/2(20-10)5=25