the number of real values of x where the function f(x) = cosx+cos{(√2)x} attains its maximum is

(a) 0

(b) 1

(c) 2

(d) infinite

Dear raman malik.

f(x) = cosx+cos{(√2)x}

f'(x)=-sin x -√2 sin √2x =0

    it gives x= 2m ∏/(√2 +1 )   and  (2m +1 ) ∏  /(√2 -1)  where m is any natural number

  clearly both values are not multiple of 2∏

only for m=0 

and f(0) = 1+1 =2 is its maximum value

so only one solution option b is correct

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