Answer:
P is exactly 3km east from the oil refinery.
Step-by-step explanation:
Let's d be the distance in km from the oil refinery to point P. So the horizontal distance from P to the storage is 3 - d and the vertical distance is 2. Hence the diagonal distance is:
So the cost of laying pipe under water with this distance is
And the cost of laying pipe over land from the refinery to point P is 400000d. Hence the total cost:
We can find the minimum value of this by taking the 1st derivative and set it to 0
We can move the first term over to the right hand side and divide both sides by 400000
From here we can square up both sides
d = 3
So the cost of pipeline is minimum when P is exactly 3km east from the oil refinery.
