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A cylinder has radius r cm and heigt h cm.

The surface area = 250cm^2

Find it's volume

The surface area = 250cm^2

Find it's volume

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#2

(Original post by

A cylinder has radius r cm and heigt h cm.

The surface area = 250cm^2

Find it's volume

**nas7232**)A cylinder has radius r cm and heigt h cm.

The surface area = 250cm^2

Find it's volume

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#3

**nas7232**)

A cylinder has radius r cm and heigt h cm.

The surface area = 250cm^2

Find it's volume

0

missed a bit out

v = 125r - (pir^3)/2

show how it is that ^^

my guess would be...

find the surface area then integrate it. But im not sure im doing it right.

v = 125r - (pir^3)/2

show how it is that ^^

my guess would be...

find the surface area then integrate it. But im not sure im doing it right.

0

but v = 125r - pir^3/2

I just don't know to get it

i guess:

surface area = 250

250 = 2pir

125 = pi r

125r = pir^2

the reason i cant do it is because i dont know the method of working out the area of the cylinder lol

I just don't know to get it

i guess:

surface area = 250

250 = 2pir

125 = pi r

125r = pir^2

the reason i cant do it is because i dont know the method of working out the area of the cylinder lol

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#7

1) Πr^2 * h= V

Πr^2 + 2Πr*h =250

2) h = (250-Πr^2) / 2Πr

Sub 2) into 1)…

Πr^2 * (250-Πr^2) / 2Πr = V

r(250-Πr^2)=V

250r – Πr^3 = V

(divide by 2)

125r – (Πr^3)/2 = V

Πr^2 + 2Πr*h =250

2) h = (250-Πr^2) / 2Πr

Sub 2) into 1)…

Πr^2 * (250-Πr^2) / 2Πr = V

r(250-Πr^2)=V

250r – Πr^3 = V

(divide by 2)

125r – (Πr^3)/2 = V

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#8

hope that helps...area is equal= the area of a circle + circumference*height(this is the outer surface area)....Πr^2 + 2Πr*h

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(Original post by

1) Πr^2 * h= V

Πr^2 + 2Πr*h =250

2) h = (250-Πr^2) / 2Πr

Sub 2) into 1)…

Πr^2 * (250-Πr^2) / 2Πr = V

r(250-Πr^2)=V

250r – Πr^3 = V

(divide by 2)

125r – (Πr^3)/2 = V

**fisfos815**)1) Πr^2 * h= V

Πr^2 + 2Πr*h =250

2) h = (250-Πr^2) / 2Πr

Sub 2) into 1)…

Πr^2 * (250-Πr^2) / 2Πr = V

r(250-Πr^2)=V

250r – Πr^3 = V

(divide by 2)

125r – (Πr^3)/2 = V

250r – Πr^3 = V

(divide by 2)

125r – (Πr^3)/2 = V

if you divide by two then you will get

125r – (Πr^3)/2 = V/2

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#10

Also for the surface area you need to do the area of the body - which you correctly identified as 2pirh , but then you need to add on the top AND bottom of the cylinder (Im pretty sure you only add on one end), this would make the surface area of the Cylnder:

SA = 2pirh + 2pir^2

i think thats right.....

SA = 2pirh + 2pir^2

i think thats right.....

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#12

SA: 2 pi rh + pi r^2 = 250 (when surface area excludes the top of the cylinder)

V: pi r^2 h therefore h= v/ (pi r^2)

put the rearranged V formula into the SA formula to get:

2 pi r [v/(pi r^2)] + pi r^2 = 250

cancel out that fraction:

2V / r + pi r^2 = 250

multiply by r:

2V + pi r^3 = 250r

divide by 2:

V + (pi r^3)/2 =125 r

rearrange to get answer....

viola - dont understand why surface area of cylinder would mean the side and bottom but not the top tho....

V: pi r^2 h therefore h= v/ (pi r^2)

put the rearranged V formula into the SA formula to get:

2 pi r [v/(pi r^2)] + pi r^2 = 250

cancel out that fraction:

2V / r + pi r^2 = 250

multiply by r:

2V + pi r^3 = 250r

divide by 2:

V + (pi r^3)/2 =125 r

rearrange to get answer....

viola - dont understand why surface area of cylinder would mean the side and bottom but not the top tho....

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