Question

Find the surface area

Answer 1

and this

Answer 2

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?

Answer 3

so i have to divide 1.8 by 2

Answer 4

correct because radius is half the diameter

Answer 5

i got 0.9

Answer 6

now substitute that in for r in SA formula

Answer 7

ok i am doing it right now

Answer 8

i did the volume then i got 0.972pi

Answer 9

correct for volume
i thought we were doing surface area

Answer 10

yea but my homework say to find both of them

Answer 11

oh ok
what would SA be then

Answer 12

3.24pi

Answer 13

good job
for next one do the same thing except at the end we will divide by 2 because its only half a sphere

Answer 14

what do you mean?

Answer 15

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

Answer 16

i find the volume is 1152pi

Answer 17

correct

Answer 18

SA is 432pi right?

Answer 19

no i get 288pi
SA = 4pi*12^2 = 4pi*144 = 576pi
take half of 576
288

Answer 20

ok thank here the another question:
The shaded circle at right has area 40π cm2. Find the surface area of the sphere.

Answer 21

i dont understand how are the circle and sphere related?

Answer 22

here the hint:The surface area of a sphere is how many times the area of a circle with the same radius?

Answer 23

ok so they share the same radius
is the entire circle shaded?

Answer 24

here the picture

Answer 25

ok thanks
use area of circle formula to find radius, then plug that into SA formula
A = pi*r^2 = 40pi

Answer 26

i have to divide pi in both side

Answer 27

yes

Answer 28

i find the raidus 6.32455532

Answer 29

correct

Answer 30

SA=4pi*(6.32)^2

Answer 31

159.7pi

Answer 32

correct and you can round up to 160 since we rounded the radius

Answer 33

Find the volume of a sphere whose surface area is 64π cm2.

Answer 34

first find radius
4pi*r^2 = 64pi

Answer 35

4

Answer 36

good
now use that to find volume
V = 4/3pi*r^3

Answer 37

i got 256pi over 3

Answer 38

correct

Answer 39

Find the surface area of a sphere whose volume is 288π cm3.

Answer 40

same thing we just did except use volume formula to find radius
V = 4/3pi*r^3 = 288pi

Answer 41

what should i do with 4/3 pi?

Answer 42

well first get rid of pi by dividing pi on both sides like last time
then we will divide by 4/3

Answer 43

x by 3/4 by both side

Answer 44

correct

Answer 45

what about 288*3/4

Answer 46

think of it as (288*3)/4

Answer 47

i got 6 as radius

Answer 48

correct put that in SA formula

Answer 49

144pi

Answer 50

correct

Answer 51

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?

Answer 52

you can do this one, its just using the formula for circle area and SA
the radius is just r

Answer 53

ok i will but i need to leave right but i tell you when i get home

Answer 54

k

Answer 55

ok i'm back so my homewprk paper has Agreat cicrle=,Shemisphere= and SA Hemisphere=__xA of great circle

Answer 56

yes lets fill in the gaps
A = area circle
SA = area circle + 1/2 SA of sphere

Answer 57

the area of that is pir^2

Answer 58

good
A = pir^2

Answer 59

we know the radius is r so that mean..

Answer 60

whats SA of sphere

Answer 61

4pir^2

Answer 62

good
SA hemishere = pir^2 +(1/2)*4pir^2
add like terms

Answer 63

3pir^2

Answer 64

good
and A = pir^2 right?
so SA = ___ * A

Answer 65

what the of Agreat cicrle= and Shemisphere=

Answer 66

i forgot to put answer

Answer 67

A = pir^2
SA hemishere = pir^2 +(1/2)*4pir^2 add like terms

Answer 68

so that is the answer or i have to solve it

Answer 69

no thats the answer, remember we dont know what r is

Answer 70

oh ok so SA = r * A

Answer 71

well does that sense?
sub in what we know
SA = 3pir^2 and A=pir^2
3pir^2 = r*pir^2
is that true?

Answer 72

not really

Answer 73

ok look at it this way
SA = 3pir^2
if i plug in A for pir^2
i get SA = 3A

Answer 74

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?

Answer 75

ok use what we just learned
SA = 3A = 4 gal + gal for the floor

Answer 76

rid of a and 5 gal

Answer 77

sorry i was unclear there
we dont know num of gall for the floor, lets call it x

Answer 78

ok

Answer 79

we know SA of top is 2*pir^2
SA = 2pir^2 = 2A

Answer 80

2A = 4 gall

Answer 81

then divide by 2

Answer 82

A = 2 gal

Answer 83

yes

Answer 84

total = 3A
A = 2 gall
so total = 3*2 = 6 gallons

Answer 85

i got it thank you so much

Answer 86

your welcome

Answer 87

if i need help for my homework can u help me

Answer 88

yeah if you post it and im on sure

Answer 89

thank again ^_^ that help me a lot from you