Any value of x such that f(x) = 0 is called a zero of the function.
Only at the zeros can the function change from being positive to negative
or vice versa. However, the function does not have to change at the zeros.
What is important is the order of the zero. If x = a is a zero of f,
and f can be written as a product of factors with 
as one of the
factors, then the value of n will tell you whether the function changes
sign at that zero. If n is odd, the sign changes, if it is even, the
sign remains the same. As an example, notice that 
. Thus, the function has a zero at x = 0. Since n = 2 in this
case, the zero is even and the sign does not change.