Applications Of Derivatives Question 293
Question: The number of values of x where the function $ f(x)=\cos x+\cos (\sqrt{2}x) $ attains its maximum is
[IIT 1998; DCE 2001, 05]
Options:
A) 0
B) 1
C) 2
D) Infinite
Show Answer
Answer:
Correct Answer: B
Solution:
$ f(x)=\cos x+\cos (\sqrt{2}x) $
$ f’(x)=-\sin x-\sqrt{2}\sin (\sqrt{2}x)=0 $
Hence $ x=0 $ is the only solution. $ f’’(x)=-\cos x-2\cos (\sqrt{2}x)<0 $ at $ x=0 $
Hence maxima occurs at $ x=0 $ .
BETA
