a ladder leans against a vertical wall with the bottom of the ladder 8 ft from the wall on a horizontal floor. at that time the bottom end of the ladder is being pulled away at the rate of 3ft/s and the top of the ladder slips down the wall at a rate of 4 ft/s. how long is the ladder?

Question

anonymous · Answer

look a related rate ladder problem.  
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anonymous · Answer

$$z^2=x^2+y^2$$
$$0=2xx'=2yy'$$
$$0=xx'+yy'$$ put 
$$x=8,x'=3,y'=4$$ and solve for y
then get the length of the ladder by pythagoras
btw the left hand side is 0 because the length of the ladder is constant