First slide
Functions (XII)
Question

The period of the function 3sin2πx+x[x]+sin4πx, where [⋅] denotes the greatest integer function is 503kthen k=

Moderate
Solution

sin2πx=1cos2πx2
Since cos 2πx is a periodic function with period 2π2π=1, 
therefore sin2πx is periodic with period 1.    (1)
x – [x] is a periodic function with period 1.    (2)
sin4πx=sin2πx2=14(1cos2πx)2 =141+cos22πx2cos2πx=18(3+cos4πx4cos2πx)
Since, cos 4πx is a periodic function with period 2π4π
= 1/2and cos 2πx is a periodic function with period
2π2π=1, therefore, period of sin4πx is equal to
 L.C.M. 1,12= L.C.M. (1,1) H.C.F. (1,2)=11=1
From Eq. (1), (2) and (3), we get
Period of 3sin2πx+x[x]+sin4πx=1

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