need help...

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- November 5th 2006, 09:58 PMbobby77minimum value
need help...

- November 5th 2006, 10:31 PMearboth
Hello, bobby,

I label the island I.

The total distance is d = IC + CD

The total energy is e = 2*IC + CD

Let BC = x

Then you can calculate the energy by:

You'll get the minimum if e'(x) = 0. So you need first the derivative of e (use chain rule!):

Now e'(x) = 0:

. Multiply both sides by the denominator and afterwards square both sides:

. Solve for x. You'll get 2 values for x. The negative one is senseless in the described situation.

I got

EB