Posted by **angel** on Thursday, April 5, 2012 at 7:49am.

A____________B 9 miles is between A and B?

at 3pm Andy began travelling South at a rate of 4mi/hr from point A

at the same time Bill began travelling West at a rate of 5mi/hr from point B to A

both stop wlking when Bill reaches point A

What time will the distance between Bill and Andy be minimized?

- calc -
**Steve**, Thursday, April 5, 2012 at 12:03pm
Let A be (0,0) and B = (9,0)

The distance d between Bill and Andy after h hours can be found using

d^2 = (4h)^2 + (9-5h)^2

= 16h^2 + 81 - 90h + 25h^2

= 41h^2 - 90h + 81

d = √(41h^2 - 90h + 81)

dd/dh = (82h - 90)/√(41h^2 - 90h + 81)

dd/dh = 0 when h = 90/82 = 1.1 hr = 1:06

3:00 + 1:06 = 4:06

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