by **Takuto** » Sun Dec 05, 2004 12:12 am

Very nice! Keep up the great work.

A train leaves the station, going south, at 2:00 pm at a constant speed of 80 km/h. Another train, going north, reaches that same station at 3:00 pm at a constant speed of 60 km/h. When will the trains be closest to each other? <-- Why are people scared of this? Perhaps it's because it requires Calculus!

d(x) = sqrt((60 - 60x)^2 + (80x)^2)

So:

d'(x) = (1/2)(10000x^2-7200x+3600)^(-1/2)(20000x -7200)

To determine the possible critical points - let d'(x)=0 --> The trains will be closest together at 2:21.40 pm.

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