The depth of water in an experimental filtration vessel, D D\,D centimetres, varies according to the radius of the sediment layer r r\,r millimetres, such that D=(2r3+9r2)4D = (2r^3 + 9r^2)^4D=(2r3+9r2)4. Determine the rate of change of the depth with respect to the radius, dDdr\displaystyle \frac{dD}{dr}drdD.
133 exam-style questions on WJEC A Level Maths 3.6.5 Differentiation (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.