If 0 ≤ x ≤ 2π, which equation is a line of symmetry for the graph of y = cos x?

Question

x = 0
x = 2π
x = π
y = 0

Answer 1

y = 0

The graph of y = cos x is symmetrical about the y axis.

Answer 2

y=0 is not the y-axis.

And anyway, in the stated domain, x=pi is the axis of symmetry.