The number of values of x where the function f(x) = 2 (cos 3x + cos √3x attains its maximum, is
A
1
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B
2
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C
0
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D
Infinite
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Solution
The correct option is A
1
We have, f(x)=2(cos3x+cos√3x)=4cos(3+√32)xcos(3−√32)x⩽4 and it is equal to 4 when both cos (3+√32)xandcos(3−√32) Are equal to 1 for a value of x. This is possible only when x = 0. Hence (a) is the correct answer.