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 $
