If f:R→R is defined by f(x)=x−[x]−12for x∈R, where [x] is the greatest integer not exceeding x, then x∈R:f(x)=12=
Z
N
ϕ
R
0≤x−[x]<1⇒−12≤x−[x]−12<12
⇒−12≤f(x)<12⇒f(x)≠12∀x
⇒ x∈R:f(x)=12=ϕ