The movement of a certain glacier can be modelled by [tex]d(t)=0.01t^2+0.5t[/tex] where d is the distance in metres that a stake on the glaciers has moved, relative to a fixed position, t days after measurements began. Find the rate at which the glacier is moving after 20 days. What is the question asking for? I got an answer by using: lim_h-0 f(a+h)-f(a)/h and I got a final answer of 8.5 but the answer is 0.9m/day in the book !!!