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Topic:  teacher needs help! 
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Subject:  RE: teacher needs help! 
Author:  Chuck 
Date:  Dec 14 2004 
This is a standard rates problem using the distance formula. If y is the car's
distance north of the intersection, and x the truck's distance east, then the
distance between the two is s^2 = x^2 + y^2.
Using implicit differentiation, 2ss' = 2xx' + 2yy', and at t=2 hr, x = 90mi, y =
120mi, s = 150mi, x' = 45mph and y'=60mph. Then s' = 150 mph.
Dr. Math can give good help on these kind of problems.
 
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