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Rate of change of the area of the rebgion 
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#1
Nov1012, 10:16 PM

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1. The problem statement, all variables and given/known data
A board 5 feet long slides down a wall. at the instant the bottom end is 4 feet from the wall, the other end is moving down the wall the rate of 2 feet per second.at that moment how fast is the area of the region between the board, the ground and the wall changing? 2. Relevant equations a=1/2bh 3. The attempt at a solution x^2 + 4^2= 5^2 x=3 da/dt= 1/2b(db/dt)(dh/dt) I think i started it up wrong and I don't know where to go next.. 


#2
Nov1112, 01:03 AM

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#3
Nov1112, 01:42 AM

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just a normal triangle drawn on a line like a typical triangle leaning against a wall problem.



#4
Nov1112, 01:49 AM

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Rate of change of the area of the rebgion
Neither end of the board is touching the ground, so it's not a triangle.



#5
Nov1112, 01:49 AM

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#6
Nov1112, 01:26 PM

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that is how it looks 


#7
Nov1112, 01:44 PM

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When you said x=3, that should be h=3 . In general, how are b and h related, considering that they're legs of a right triangle? 


#8
Nov1212, 12:50 AM

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i said b= 4ft and h=3 ft



#9
Nov1212, 12:57 AM

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(Use the Pythagorean theorem.) 


#10
Nov1212, 12:19 PM

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Thanks
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RGV 


#11
Nov1212, 01:04 PM

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It should have said: That's what b & h are at the instant that b = 4 ft, but how are they related in general? 


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