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If `f(x)+2f((1)/(x))=3x,x ne 0`, and `S={x in R : f (-x)},` then S:A. is an empty setB. contains exactly one elementC. Contains exactly two elements .D. contains more than two elements

Answer» Correct Answer - C
We have,
`f(x)+2f((1)/(x))=3x" " `….(i)
Replacing x by `(1)/(x)`, we get
`f((1)/(x))+2f(x)=(3)/(x)" " `….(ii)
Solving (i) and (ii) , we obtain
`f(x)=3((2)/(x)-x)`
`:. f(x)=f(-x)`
`implies 3((2)/(x)-x)=3(-(2)/(x)+x)`
`implies (4)/(x)-2x=0implies 2x^(2)-4=0implies x=pm sqrt(2)`
Hence , `S={x in R: f(x)=f(-x)}={-sqrt(2), sqrt(2)}`


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