Even and odd functions are similar in the fact that they are both functions. However they are also different. Even functions are reflective over an axis, odd functions are not. A function is odd if the highest exponent is odd: y=2x^5+3x^2-x+2. A function is even if the highest exponent is even: y=x^2+2x-5. Every even function must have the characteristic that for every negative x value, f(-x)=f(x). A function can only be even if this statement is true. Every odd function must have the characteristic that for every negative x value, f(-x)=-f(x). Just as for even, a function can only be odd if this statement is true.