Can some one check my work? Related Rates

1. Nov 16, 2011

nyr

The problem is:
For the baseball diamond in exercise 33, suppose the player is running from first to second at a speed of 28 feet per second. Find the rate at which the distance from home plate is changing when the player is 30 feet from second base.
(the picture basically shows a square with 90 ft sides)

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My solution

Given: dy/dt = 28 ft/sec
Find: ds/dt when x=30

902y2=s2
0 +2y(dy/dt)=2s(ds/dt)
2(60)(28)=2(30√13)(ds/dt)
56/(√13) ft/sec=ds/dt
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I'm not really sure if its the correct answer because I always seem to mix up negative signs and I wasnt sure if this required one.
If you really need to see the picture its found here:
http://books.google.com/books?id=E5...he player is 30 feet from second base&f=false
Page 151 #34

2. Nov 16, 2011

Staff: Mentor

It looks like you left out the + sign on the left side. The equation should be
902 + y2=s2
Looks fine to me.