# A cone has a volume of 562.5 pi cm^3 PLS HELPPP

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A cone has a volume of 562.5 pi cm^3

The radius of the base of the cone is equal to twice the height of the cone

Work out the cufrved surface area of the cone

Answer correct to 3 significant figures

i'm very stuck

The radius of the base of the cone is equal to twice the height of the cone

Work out the cufrved surface area of the cone

Answer correct to 3 significant figures

i'm very stuck

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#2

(Original post by

A cone has a volume of 562.5 pi cm^3

The radius of the base of the cone is equal to twice the height of the cone

Work out the cufrved surface area of the cone

Answer correct to 3 significant figures

i'm very stuck

**joe.bbbbbbbbbbbb**)A cone has a volume of 562.5 pi cm^3

The radius of the base of the cone is equal to twice the height of the cone

Work out the cufrved surface area of the cone

Answer correct to 3 significant figures

i'm very stuck

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(Original post by

Do you know the formulae for the volume and surface area of a cone (Google / maths book / ...)

**mqb2766**)Do you know the formulae for the volume and surface area of a cone (Google / maths book / ...)

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#4

(Original post by

yeah but i have no clue how to use it in this question

**joe.bbbbbbbbbbbb**)yeah but i have no clue how to use it in this question

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(Original post by

You know h=r/2 and V=562.5. That means you can find the radius of the base (and hence height) and so plug into the surface area formula.

**mqb2766**)You know h=r/2 and V=562.5. That means you can find the radius of the base (and hence height) and so plug into the surface area formula.

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#6

How about writing down the volume formula and using the two facts mentioned. You have a single equation in r which can be solved. If you're having difficulty, upload what you've done and state clearly what you're having problems with.

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(Original post by

How about writing down the volume formula and using the two facts mentioned. You have a single equation in r which can be solved. If you're having difficulty, upload what you've done and state clearly what you're having problems with.

**mqb2766**)How about writing down the volume formula and using the two facts mentioned. You have a single equation in r which can be solved. If you're having difficulty, upload what you've done and state clearly what you're having problems with.

dont u need height number to solve radius

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**mqb2766**)

How about writing down the volume formula and using the two facts mentioned. You have a single equation in r which can be solved. If you're having difficulty, upload what you've done and state clearly what you're having problems with.

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#9

(Original post by

radius is sqrt 3V/pi h

**joe.bbbbbbbbbbbb**)radius is sqrt 3V/pi h

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(Original post by

You've not substituted h=r/2 to get an equation in just r.

**mqb2766**)You've not substituted h=r/2 to get an equation in just r.

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#11

(Original post by

r = sqrt 3V/pi hx2

**joe.bbbbbbbbbbbb**)r = sqrt 3V/pi hx2

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(Original post by

It would help to see your working. If you replace h with r/2, there will be no h in this equation. That is the whole point of doing it.

**mqb2766**)It would help to see your working. If you replace h with r/2, there will be no h in this equation. That is the whole point of doing it.

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(Original post by

oh ok

**joe.bbbbbbbbbbbb**)oh ok

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#14

(Original post by

how do i solve it now though

**joe.bbbbbbbbbbbb**)how do i solve it now though

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#16

You can't solve that as r appears on both sides of the equation. Also you're told what V is?

Do the substitution h=r/2 in the V=... formula before you rearrange the equation to get r=...

Do the substitution h=r/2 in the V=... formula before you rearrange the equation to get r=...

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#18

(Original post by

so i just need to rearrange the equation to have r on one side?

**joe.bbbbbbbbbbbb**)so i just need to rearrange the equation to have r on one side?

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(Original post by

Yes. That's what you always try to do.

**mqb2766**)Yes. That's what you always try to do.

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