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September 16, 2014

September 16, 2014

Posted by **kait** on Sunday, September 25, 2011 at 12:13am.

- diffirential calculus -
**Reiny**, Sunday, September 25, 2011 at 10:39amdid you make a diagram?

let her distance from the lightpole be x ft

let the length of her shadow be y ft

by similar triangles ...

6/y = 10/(x+y)

6x + 6y = 10y

6x = 4y

6 dx/dt = 4 dy/dt

we are given: dx/dt + dy/dt = 2 ft/sec

dx/dt = 2 - dy/dt

so

6(2 - dy/dt) = 4 dy/dt

12 - 6dy/dt = 4dy/dt

12 = 10dy/dt

dy/dt = 12/10 = 1.2 ft/sec

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