The set of points of continuity when f(x)={1ifx is rational−1ifx is irrational
R
φ
(−1, 1)
R+
f(x)={1ifx is rational−1ifx is irrational
between two rational numbers there are infinite irrational numbers and
between two irrational numbers there are infinite rational numbers.
Clearly f(x)is discontinuous every where
Set of points of continuous=ϕ