I'm a little bit stuck with part of one of my examples:

We need to find the minimum distance, so we need to differentiate this. To do so, let's use the chain rule. Let U = 900 - 5400t + 11700t2 Then du dt = -5400 + 23400t and D = Vu SO dD 1 du =5 This gives dD -5400 + 23400t dt 2 900 - 5400t + 11700t2 11700t - 2700 V900 - 5400t + 11700t2