Question

How to determine whether a function is odd or even?

Answer 1

That's very important, so I hope it helps:
f(-x)=f(x) if it is even (y axis folding is the same, like cos(x), or y=x^2)
f(-x)=-f(x) if it is odd(Symmetry wrt the origin, for instance, sin(x), or simply y=x!)