show that U is a subspace of the given vetor space V.

V = F(R), ( the set of all functions from R into R) , U is the set of all even functions in V.

I am really stuck on this, if U is the set of all even functions in V, than x^2 must be in U? hence the set is non-empty, but i am not sure how to show that U is a subspace of V.

I know I have to show that if you take two elements from U and add them you should still get an element in U, but dont know how to go about it?

Any help appreciated.

thank you