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    The slant height of a cone is 18cm find the volume of the cone in terms of h, the perpendicular height from the base ....my working:
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    I think my method is completely flawed

    how should I do it? I am trying to work out the perpendicular height by Pythagoras theorem but it looks to messy
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    (Original post by madfish)
    The slant height of a cone is 18cm find the volume of the cone in terms of h, the perpendicular height from the base ....my working:
    You are trying to express the volume in terms of h.
    Why have you expressed h in terms of r?
    I'd suggest starting over.
    Hint: r2 = 182 - h2
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    (Original post by joostan)
    You are trying to express the volume in terms of h. Why have you expressed h in terms of r?
    I'd suggest starting over.
    Hint: r2 = 182 - h2
    okay so v= 324pir^2 - pir^2h^2 all over 3

    how on earth to I differentiate that?
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    (Original post by madfish)
    okay so v= 324pir^2 - pir^2h^2 all over 3

    how on earth to I differentiate that?
    You've still got r's in the equation . . .
    They need getting rid of, though you're pretty close
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    (Original post by joostan)
    You've still got r's in the equation . . .
    They need getting rid of, though you're pretty close
    ehh I um sure of how to do the next part, would you mind helping?(I am self teaching) :/
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    (Original post by madfish)
    ehh I um sure of how to do the next part, would you mind helping?(I am self teaching) :/
    Just a little help, nothing too grand. . .

    r2 = 182 -h2
    Sub this in to 1/3 pi*r2h
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    (Original post by joostan)
    Just a little help, nothing too grand. . .

    r2 = 182 -h2
    Sub this in to 1/3 pi*r2h
    okay so v= 1/3 (324pih-pih^3) ?
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    (Original post by madfish)
    okay so v= 1/3 (324pih-pih^3) ?
    Correct though you could factor out pi*h if you were really keen
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    (Original post by joostan)
    Correct though you could factor out pi*h if you were really keen
    i just differentiated this to get 108pi -pih^2

    correct?:P
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    (Original post by madfish)
    i just differentiated this to get 108pi -pih^2

    correct?:P
    Yes
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    (Original post by joostan)
    Yes
    thanks man appreciated
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    (Original post by madfish)
    thanks man appreciated
    De nada
 
 
 
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