Question

The number of values of $x$ where the function $f\left(x\right)=\cos x+\cos \left(\sqrt{2}x\right)$ attains its maximum is

• A. 0
• B. 1
• C. 2
• D. infinite

Answer 1

Answer: (B)

1

$f^{\prime }\left(x\right)$ $=-sinx-\sqrt{2}sin\left(\sqrt{2}x\right)$
$=0$
Hence $x=0$
Hence maximum value will be attained at $x=0$
$f\left(0\right)=2$.
Maximum value is 2

Therefore, only one value of $x$ exists.