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Math Help - related rates problem

  1. #1
    Junior Member
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    related rates problem

    A leadder 25ft long is leaning against the wall of a hour. The base of the ladder is pulled away from the wall at a rate of 2ft/sec

    (my picture isnt to scal for some reason)

    |\
    r | \ 25ft
    | \
    |----\
    7ft

    a.) How fast is the top of the ladder moving down the wall when it's base is 7ft from the wall?


    i understand i can do pythag. theorom to get side of r which is 24 but im unsure of how to find dr/dt? do i still use pythag. theorom to solve for dr/dt? if so im unsure how to do it....any explanation would be greatfull!
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  2. #2
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    Quote Originally Posted by maybnxtseasn View Post
    A leadder 25ft long is leaning against the wall of a hour. The base of the ladder is pulled away from the wall at a rate of 2ft/sec

    (my picture isnt to scal for some reason)

    |\
    r | \ 25ft
    | \
    |----\
    7ft

    a.) How fast is the top of the ladder moving down the wall when it's base is 7ft from the wall?


    i understand i can do pythag. theorom to get side of r which is 24 but im unsure of how to find dr/dt? do i still use pythag. theorom to solve for dr/dt? if so im unsure how to do it....any explanation would be greatfull!
    Think of the side r as a function of x.

    r^2=(25)^2-x^2

    2r\frac{dr}{dt}=2x\frac{dx}{dt}

    \frac{dr}{dt}=\frac{x}{r}\frac{dx}{dt}
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