Find the Taylor series of f(x) = x^(-2) at a = 1

I know how to do this, simply by using the formula for Taylor series. However in cases like this when the nth derivative of f(x) does not reach zero for finite values of n, how do you know how many terms to use? The question does not specify how many terms to add, nor does it specify an error. All I'm wondering is if the number of terms to use is for me to decide, or if there is a correct number of terms I must use.