a simple model for the cost of a car journey £C when a car is driven at a steady speed of v mph is?
c = 4500/v + v + 10

a) find value of v which minimises cost of the journey.

b) use d^2C/dv^2 to verify C is a minimum for this value of v
c) calculate minimum cost of the journey
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answers:
Steve A say: c = 4500/v + v + 10
c' = -4500v^(-2) +1
0 = -4500v^(-2) +1
4500 = v^2
v = 30√5 = 67.08

c'' = 9000v^(-3)
0 = 9000v^(-3)
0 = v

c = £144.16
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lbnzz say: ryafejxc
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alex say: Hint:
a/
dc/dv=0
b/
d^2C/dv^2 >0
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qobyb say: mrbsxtld
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