# I NEED HELP =( This assignment is graded.

1. Oct 13, 2004

### shreena03

An underground telephone cable is to be laid btwn 2 boathourses on opposite banks of a straight river. One boathouse is 600 meters downstream from the other. The river is 200 meters wide. If the cost of laying cable is $150 per metere underwater and$80 per metere on land, how should the cable be laid to minimize cost?

Can someone help me figure this out and show how they did it?

Thank u so much if u can.

Last edited: Oct 13, 2004
2. Oct 13, 2004

### Integral

Staff Emeritus
It is not the policy of this site to simply do homework for people. You will not be able to come here to request a solution during your test.

What you need to do is find an expression for the total length of the wire. Consider that you must cross the river, so start by drawing yourself a picture of the situation. Can you find an expression for the distance across the river in terms of the distance along the shore. You have all the information required to do this.

Show us what you are thinking.

3. Oct 13, 2004

### singleton

Think of it this way.

Draw a diagram. Think of the possibilities. There are really three. Do you take the hypotenuse route straight to it? Or do you go directly across the water, then along the opposite side?

Or perhaps you land somewhere between and carry on the rest from that point?

Find an equation. What are you looking for? The cost of it. What do you want to do? Minimize or maximize?