Question

Which of the following functions is periodic?


Select an answer

A.
f(x) = cos(x)


B.
f(x) = 3x + 1


C.
f(x) = x^2


D.
f(x) = ln(x)

Answer 1

A. f(x) = cos(x)

Reason: cos(x) is periodic with period 2π (cos(x + 2π) = cos x for all x).
3x+1 and x^2 are unbounded and not repeating, and ln(x) is monotonic on its domain, so none of those are periodic.