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# C2 help, pic provided watch

1. 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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2. 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
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
4. (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?
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
6. (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) :/
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
8. (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) ?
okay so v= 1/3 (324pih-pih^3) ?
Correct though you could factor out pi*h if you were really keen
10. (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
i just differentiated this to get 108pi -pih^2

correct?:P
Yes
12. (Original post by joostan)
Yes
thanks man appreciated
thanks man appreciated

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