## marigirl one year ago Can you help me find an expression for h please

1. marigirl

2. marigirl

SO far i have $\frac{ 40-x }{ r }=\frac{ 40 }{ 20 }$

3. phi

assuming h is the height of the cylinder

4. marigirl

What must the radius of the cylinder be to give the cylinder the maximum volume is my question..

5. marigirl

$v=\pi r^2 h$ so an expression to sub into h

6. phi

I am not awake! the proportion is $\frac{40-h}{r}= \frac{40}{20}$

7. marigirl

ok great so i was on the right track. ill go ahead and differentiate now :)

8. marigirl

why did u choose 40-h .....where as i did 40-x

9. marigirl

or are we talking about the same things?

10. phi

it depends what you mean by "x" I used h because h is the height of the cylinder

11. marigirl

so then when you did 40-h you meant 40-height of cylinder...so we are left with the top part of cylinder

12. phi

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13. phi

once we have that relation we can solve for h $\frac{40-h}{r}= 2 \\ 40-h= 2r \\ h= 40-2r$

14. marigirl

oh yup i get it now. thanks heaps!