For which of the following functions is it true that -f(x)=f(-x) for all values of x?

A) f(x)=x+4
B )f(x)=x^2+4
C) f(x)=x^3+4
D) f(x)=x^2+x
E) f(x)=x^3+x

This is a Subject Test question, right?

A useful thing to know is that –f(x) = f(–x) will be true only when a function is symmetrical about the origin. That’s only true for choice E.