JEE Main Solved Paper 2017 Question 14
Question: Twenty meters 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 :- [JEE Main Solved Paper-2017]
Options:
A) 30
B) 12.5
C) 10
D) 25
Show Answer
Answer:
Correct Answer: D
Solution:
Total length $ =r+r+r\theta =20 $
$ \theta =\frac{20-2r}{r} $
$ Area=\frac{1}{2}r^{2}\theta =\frac{1}{2}r^{2}( \frac{20-2r}{r} ) $
$ A=10r-r^{2} $ $ \frac{dA}{dr}=0 $
$ 10-2r=0, r=5 $ $ A=50-25=25 $
