12. The number of values of $x$ where the function $f ( x ) = \cos x + \cos ( \sqrt { } 2 x )$ attains its maximum is : (A) 0 (B) 1 (C) 2 (D) infinite
12. The number of values of $x$ where the function $f ( x ) = \cos x + \cos ( \sqrt { } 2 x )$ attains its maximum is :\\
(A) 0\\
(B) 1\\
(C) 2\\
(D) infinite\\