anonymous
  • anonymous
Find the surface area
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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schrodinger
  • schrodinger
I got my questions answered at brainly.com in under 10 minutes. Go to brainly.com now for free help!
anonymous
  • anonymous
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anonymous
  • anonymous
and this
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dumbcow
  • dumbcow
hello for the first one you need to use formula for SA of sphere and then plug in the radius so what is SA of a sphere? what is the radius of our sphere?

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anonymous
  • anonymous
so i have to divide 1.8 by 2
dumbcow
  • dumbcow
correct because radius is half the diameter
anonymous
  • anonymous
i got 0.9
dumbcow
  • dumbcow
now substitute that in for r in SA formula
anonymous
  • anonymous
ok i am doing it right now
anonymous
  • anonymous
i did the volume then i got 0.972pi
dumbcow
  • dumbcow
correct for volume i thought we were doing surface area
anonymous
  • anonymous
yea but my homework say to find both of them
dumbcow
  • dumbcow
oh ok what would SA be then
anonymous
  • anonymous
3.24pi
dumbcow
  • dumbcow
good job for next one do the same thing except at the end we will divide by 2 because its only half a sphere
anonymous
  • anonymous
what do you mean?
dumbcow
  • dumbcow
it shows image of half sphere with radius of 12 right? so find volume and SA using same formulas substituting 12 for r but we only want half the volume and half the SA
anonymous
  • anonymous
i find the volume is 1152pi
dumbcow
  • dumbcow
correct
anonymous
  • anonymous
SA is 432pi right?
dumbcow
  • dumbcow
no i get 288pi SA = 4pi*12^2 = 4pi*144 = 576pi take half of 576 288
anonymous
  • anonymous
ok thank here the another question: The shaded circle at right has area 40π cm2. Find the surface area of the sphere.
dumbcow
  • dumbcow
i dont understand how are the circle and sphere related?
anonymous
  • anonymous
here the hint:The surface area of a sphere is how many times the area of a circle with the same radius?
dumbcow
  • dumbcow
ok so they share the same radius is the entire circle shaded?
anonymous
  • anonymous
here the picture
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dumbcow
  • dumbcow
ok thanks use area of circle formula to find radius, then plug that into SA formula A = pi*r^2 = 40pi
anonymous
  • anonymous
i have to divide pi in both side
dumbcow
  • dumbcow
yes
anonymous
  • anonymous
i find the raidus 6.32455532
dumbcow
  • dumbcow
correct
dumbcow
  • dumbcow
SA=4pi*(6.32)^2
anonymous
  • anonymous
159.7pi
dumbcow
  • dumbcow
correct and you can round up to 160 since we rounded the radius
anonymous
  • anonymous
Find the volume of a sphere whose surface area is 64π cm2.
dumbcow
  • dumbcow
first find radius 4pi*r^2 = 64pi
anonymous
  • anonymous
4
dumbcow
  • dumbcow
good now use that to find volume V = 4/3pi*r^3
anonymous
  • anonymous
i got 256pi over 3
dumbcow
  • dumbcow
correct
anonymous
  • anonymous
Find the surface area of a sphere whose volume is 288π cm3.
dumbcow
  • dumbcow
same thing we just did except use volume formula to find radius V = 4/3pi*r^3 = 288pi
anonymous
  • anonymous
what should i do with 4/3 pi?
dumbcow
  • dumbcow
well first get rid of pi by dividing pi on both sides like last time then we will divide by 4/3
anonymous
  • anonymous
x by 3/4 by both side
dumbcow
  • dumbcow
correct
anonymous
  • anonymous
what about 288*3/4
dumbcow
  • dumbcow
think of it as (288*3)/4
anonymous
  • anonymous
i got 6 as radius
dumbcow
  • dumbcow
correct put that in SA formula
anonymous
  • anonymous
144pi
dumbcow
  • dumbcow
correct
anonymous
  • anonymous
if the radius of the base of a hemisphere (which is bounded by a great circle) is r, what is the area of the great circle? What is the total surface area of the hemisphere, including the base? How do they compare?
anonymous
  • anonymous
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dumbcow
  • dumbcow
you can do this one, its just using the formula for circle area and SA the radius is just r
anonymous
  • anonymous
ok i will but i need to leave right but i tell you when i get home
dumbcow
  • dumbcow
k
anonymous
  • anonymous
ok i'm back so my homewprk paper has Agreat cicrle=,Shemisphere= and SA Hemisphere=__xA of great circle
dumbcow
  • dumbcow
yes lets fill in the gaps A = area circle SA = area circle + 1/2 SA of sphere
anonymous
  • anonymous
the area of that is pir^2
dumbcow
  • dumbcow
good A = pir^2
anonymous
  • anonymous
we know the radius is r so that mean..
dumbcow
  • dumbcow
whats SA of sphere
anonymous
  • anonymous
4pir^2
dumbcow
  • dumbcow
good SA hemishere = pir^2 +(1/2)*4pir^2 add like terms
anonymous
  • anonymous
3pir^2
dumbcow
  • dumbcow
good and A = pir^2 right? so SA = ___ * A
anonymous
  • anonymous
what the of Agreat cicrle= and Shemisphere=
anonymous
  • anonymous
i forgot to put answer
dumbcow
  • dumbcow
A = pir^2 SA hemishere = pir^2 +(1/2)*4pir^2 add like terms
anonymous
  • anonymous
so that is the answer or i have to solve it
dumbcow
  • dumbcow
no thats the answer, remember we dont know what r is
anonymous
  • anonymous
oh ok so SA = r * A
dumbcow
  • dumbcow
well does that sense? sub in what we know SA = 3pir^2 and A=pir^2 3pir^2 = r*pir^2 is that true?
anonymous
  • anonymous
not really
dumbcow
  • dumbcow
ok look at it this way SA = 3pir^2 if i plug in A for pir^2 i get SA = 3A
anonymous
  • anonymous
oh now i got it If Jose used 4 gallons of wood sealant to cover the hemispherical ceiling of his vaction home, how many gallons of wood sealant are needed to cover the floor?
dumbcow
  • dumbcow
ok use what we just learned SA = 3A = 4 gal + gal for the floor
anonymous
  • anonymous
rid of a and 5 gal
dumbcow
  • dumbcow
sorry i was unclear there we dont know num of gall for the floor, lets call it x
anonymous
  • anonymous
ok
dumbcow
  • dumbcow
we know SA of top is 2*pir^2 SA = 2pir^2 = 2A
dumbcow
  • dumbcow
2A = 4 gall
anonymous
  • anonymous
then divide by 2
anonymous
  • anonymous
A = 2 gal
dumbcow
  • dumbcow
yes
dumbcow
  • dumbcow
total = 3A A = 2 gall so total = 3*2 = 6 gallons
anonymous
  • anonymous
i got it thank you so much
dumbcow
  • dumbcow
your welcome
anonymous
  • anonymous
if i need help for my homework can u help me
dumbcow
  • dumbcow
yeah if you post it and im on sure
anonymous
  • anonymous
thank again ^_^ that help me a lot from you

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