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# How to find radius of a hemisphere with the surface area which is 618cm?

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How to find radius of a hemisphere with the surface area which is 618cm?

Guest May 19, 2015

#6
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Zac's hemisphere and my hemisphere had a bottom on it.

Yes, I noticed. The bottom is part of the lower half of a CDD Sphere.

A hemisphere is one half of a sphere. Doubling this a sphere. If the bottom area of a hemisphere is needed then it’s calculated separately. In this case it’s 308.965cm2

Calculating the radius from a hemisphere that includes the area of the bottom returns a value that will correlate to a surface area value that is smaller than the sum of two identical hemispheres.

Our brains have ceribral hemispheres.

By way of curiosity, which half were you using?

Mine is full of grey matter. Does yours is contains nothing?

I am unsure of the color, but the callosal commissure joins two cerebral CDD hemispheres. However, in this case, the whole is greater than the sum of its parts –instead of less than. :)

Nauseated  May 20, 2015
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Sa  = 4*pi *r^2   ....so

618 = 4 * pi *r^2       divide both sides by 4 pi

618/ (4 pi) = r^2       take the positive root of both sides

CPhill  May 19, 2015
#2
+981
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Isn't the S.A. of a hemisphere:

pi*r^2 + (0.5)*4*pi*r^2 = S.A.

so . . .

3pi*r^2 = 618cm

r^2 = 618/3pi

r = sqrt(618/3pi)

r approximately = 8.0976 cm

zacismyname  May 20, 2015
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Yes Zac, I am with you :)

CPhill, you made a boo boo

Melody  May 20, 2015
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$$\displaystyle \\ \text {Surface area of a hemisphere is }\\ \noindent A_ s = 2\pi*r^2\\\ \noindent \text {Radius is }\\ r = \sqrt{\dfrac{A_s}{ 2\pi}}\hspace{30pt}| A_s=618cm^2 \\\ r = \sqrt{\dfrac{618cm^2}{ 2\pi}}\; =\; 9.917cm \\\\ \text {The other answers are \rm \pm  the upper and lower half of a CDD Sphere.}$$

Nauseated  May 20, 2015
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+94202
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Hi Nauseated,

Zac's hemisphere and my hemisphere had a bottom on it.

A hemisphere is a half of a sphere - if the sphere is solid then the hemisphere definitely has a base.

Our brains have ceribral hemispheres.

Mine is full of grey matter.   Does yours is contains nothing?

Melody  May 20, 2015
#6
+1036
+10

Zac's hemisphere and my hemisphere had a bottom on it.

Yes, I noticed. The bottom is part of the lower half of a CDD Sphere.

A hemisphere is one half of a sphere. Doubling this a sphere. If the bottom area of a hemisphere is needed then it’s calculated separately. In this case it’s 308.965cm2

Calculating the radius from a hemisphere that includes the area of the bottom returns a value that will correlate to a surface area value that is smaller than the sum of two identical hemispheres.

Our brains have ceribral hemispheres.

By way of curiosity, which half were you using?

Mine is full of grey matter. Does yours is contains nothing?

I am unsure of the color, but the callosal commissure joins two cerebral CDD hemispheres. However, in this case, the whole is greater than the sum of its parts –instead of less than. :)

Nauseated  May 20, 2015
#7
+93025
+8

LOL....!!!!

It appears that I had a "hemi - rage "  on this one......

Oh well....just proves I'm still   ....  "CDD - capable"

CPhill  May 20, 2015
#8
+94202
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# ROF LOL      ROF LOL        ROF LOL

"Calculating the radius from a hemisphere that includes the area of the bottom returns a value that will correlate to a surface area value that is smaller than the sum of two identical hemispheres."

If zac and I include the bottom OF COURSE  the  SA of the sphere will be less than the surface are of the two hemispheres.  The middle will not be included!

If you have a brick and you cut it in to 2 half bricks, the combined surface area of the 2 half bricks if greater than the surface area of the original brick!

It does not take a brain surgeon to work that out.

### Just as well because we don't have any brain surgeons around here DO WE !!

Perhaps you should go play with your cousins.  They look lonely.

Melody  May 21, 2015
#9
+981
+5

zacismyname  May 21, 2015