Applications Of Derivatives Question 279
Question: Which of the following is not a decreasing function on the interval $ ( 0,\frac{\pi }{2} ) $
Options:
A) $ \cos x $
B) $ \cos 2x $
C) $ \cos 3x $
D) $ \cot x $
Show Answer
Answer:
Correct Answer: C
Solution:
Obviously here $ \cos 3x $ is not decreasing in $ ( 0,\frac{\pi }{2} ) $ because $ \frac{d}{dx}\cos 3x=-3\sin 3x $
But at $ x=75{}^\circ ,-3\sin 3x>0 $ .
Hence the result.
BETA
