Which function families have vertical symmetry?

The functions which are even are symmetric to y-axis. By even functions, it means that f(x) = f(x) for all the domain values. Thus even functions for example, x^2, 1+x^2, cosx, x^4 all follow the conditions i.e. f(x) = f(x) and thus they are symmterical to y-axis.

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