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Questions  

If f.(0,π)R is given by f(x)=k=1n[1+sinkx],[x] denotes the greatest integer function, then the range of f(x) is

a
{n-1, n+1}
b
{n}
c
{n, n+1}
d
{n-1, n}

detailed solution

Correct option is C

f(x)=∑k=1n 1+[sin⁡kx]=n+[sin⁡x]+[sin⁡2x]+⋯+sin nx. If kx≠π2 for any k=1, 2 .........n then 0[sin⁡kx]=0,k=1,2…n. i.e. f(x)=n. If kx=π2for some k then x=π2k, hence sin⁡x,sin⁡2x,…sin⁡(k−1)x will lie between 0 and 1 so sinjx=01≤j≤k−1; sin⁡kx=1 so f(x) can be n+1 or n.

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