Differentiate (3x)e^(3x)

3e^3x + (9x)e^3x This is a good question because it involves the use of both the chain and product rules of differentiation, as well as the differential of e (all of which occur frequently in Maths A-level and in late Physics A-level). On another note, a commonly asked question by A-level students is 'why is this useful', this can be provided with a satisfactory answer in this case as Euler's number occurs so frequently in the universe and working with it is so common place.