[x]= -2

f(x)= cos [x]= cos (-2)

= cos 2

because cos(-x) = cos(x)

for-1 ≤x<0

[x]=-1

f(x)= cos[x]=cos (-1)

= cos 1

for 0 ≤x< 1

[x]=0

f(x)=cos 0 =1

for 1 ≤x<π/2

[x]=1

f(x)=cos1

Therefore, R(f) = {1, cos 1, cos 2}