This is a topic i am really struggling to get my head around.

1. the expression (x+a)^-1 can be approximated for small values of a by the relationship

(x+a)^-1 = (1/x) - (a/x^2) + (a^2/x^3)

Using the relationship, derive an expression for the rate of change of the function f(x)=1/x by the 'first principles' differentiation method.