In order to calculate the derivative of 9x^2 you must use what's called the Chain Rule. The Chain rule is a method in which people use to derive a function. In a general formula the Chain Rule states if f(x) = a*x^b then the derivative or f '(x) = a*b*x^(b-1). Given this formula as a rule of thumb, we can substitute in the numbers 9 for a and 2 for b. Following the formula we then have 9*2*x^1 which simplifies to 18x.