Q.

Which of the following function is/are periodic?

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a

fx=1,     x is  rational0,    x is  irrational

b

fx=x-x;    2n≤x<2n+112;    2n+1≤x<2n+2where [.] denotes the greatest integer function, n∈Z

c

fx=-12xπ  , where.  denotes  the   greatest   integer   function

d

fx=x-x+3+tanπx2,   where.  denotes  the    greatest   integer  function,  and a  is  a  rational  number

answer is A.

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Detailed Solution

fx=1,     x is  rational0,    x is  irrationalfx+k=1, x+k   is  rational0, x+k  is  irrational                  wherer  k   is  any  rational  number                       =1,  x  is  rational0,  x  is   irrational                       =fxTherefore, f(x) is periodic function, but its fundamental period cannot be determined. Thus,fx=x-x,    2n≤x<2n+11/2           2n+1≤x<2n+2Draw the graph from which it can be verified that period is 2.fx=-12xπor     fx+π=-12π+xπ=-12xπ+2=-12xπHence,   the  period  is  π.       fx=x-x+3+tanπx2=x-3+tanπx2x   is  periodic  withperiod  1;   tanπx2  x   is  periodic  with   period 2.Now,  the  LCM  of   1  and  2.   Hence,  the  period  of fx  is  2.
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