Posted by Anonymous on Friday, June 22, 2012 at 8:12am.
Suppose a ladder of length 36 feet rests against a wall, and we pull the base of the ladder horizontally away from the wall. For a given distance x that we pull the ladder horizontally, let g(x) be the height of the ladder on the wall, under the assumption that the other end of the ladder always contacts the wall. We know from Pythagorean theorem that for every x:
x2 + [g(x)]2 = 36^2
At what rate is the height changing when
x = 8?
When the ladder is 6 feet from the ground (g(x) = 6)?

Calculus  Reiny, Friday, June 22, 2012 at 8:23am
for easier typing, I will let y = g(x)
then x^2 + y^2 = 1296
2x dx/dt + 2y dy/dt = 0
dy/dx = x dx/dt / y
when x=8, y = √1232 or appr 35.1
dy/dx = (8/√1232)(dx/dt)
for the second part, let y = 6, then x = √1260 or appr 35.5
etc
are you sure that you were not given the rate at which the ladder was pulled away ?

Calculus  Anonymous, Friday, June 22, 2012 at 8:46am
The first part of the problem was find a formula for g'(x) in terms of
x and g(x)?
I got x/g(x)

Calculus  Reiny, Friday, June 22, 2012 at 9:00am
At what point are you in the study of related rates?
Are you not differentiating with respect to "time" ?
If not, then you would simply have
x^2 + y^2 = 1296
2x + 2y dy/dx = 0
y dy/dx = x
dy/dx = x/y or x/g(x), so that agrees with your answer.

Calculus  Anonymous, Friday, June 22, 2012 at 9:07am
I figured it out, for each part I just plug in the given x and the g(x) answer you gave me to the formula x/g(x) and simplify.
Thanks for your help!!
Answer This Question
Related Questions
 Calculus  a 5m ladder rests against a vertical wall. The top of the ladder ...
 calculus  a ladder 6 feet long leans against a vertical building. the bottom of...
 calculus helpppp!  a 20m ladder rests vertically against the side of a barn. a ...
 phsics  uniform ladder 25 ft long rests against a smooth vertical wall. The ...
 algebra  A ladder is resting against a wall. The top of the ladder touches the ...
 Calculus Ladder Problem  A ladder 20 ft long rests against a vertical wall. Let...
 Math Calculus  A 20 foot ladder is sliding down a vertical wall at a constant ...
 Math Calculus  A 20 foot ladder is sliding down a vertical wall at a constant ...
 Math Calculus  A 20 foot ladder is sliding down a vertical wall at a constant ...
 Math Calculus  A 20 foot ladder is sliding down a vertical wall at a constant ...
More Related Questions