We know that if two functions f(x) and g(x) are continuous then {f(x) +g(x)},{f(x)-g(x)}, {f(x).g(x)} and are continuous.
Since, f(x) = 2x and are polynomial functions, they are continuous everywhere.
⇒ {f(x) +g(x)},{f(x)-g(x)}, {f(x).g(x)} are continuous functions.
for,
now, f(x) = 0
⇒ 4x = 0
⇒ x = 0
∴ is discontinuous at x=0.