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anonymous

  • 5 years ago

Find the surface area

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  1. anonymous
    • 5 years ago
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  2. anonymous
    • 5 years ago
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    and this

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  3. dumbcow
    • 5 years ago
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    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?

  4. anonymous
    • 5 years ago
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    so i have to divide 1.8 by 2

  5. dumbcow
    • 5 years ago
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    correct because radius is half the diameter

  6. anonymous
    • 5 years ago
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    i got 0.9

  7. dumbcow
    • 5 years ago
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    now substitute that in for r in SA formula

  8. anonymous
    • 5 years ago
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    ok i am doing it right now

  9. anonymous
    • 5 years ago
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    i did the volume then i got 0.972pi

  10. dumbcow
    • 5 years ago
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    correct for volume i thought we were doing surface area

  11. anonymous
    • 5 years ago
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    yea but my homework say to find both of them

  12. dumbcow
    • 5 years ago
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    oh ok what would SA be then

  13. anonymous
    • 5 years ago
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    3.24pi

  14. dumbcow
    • 5 years ago
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    good job for next one do the same thing except at the end we will divide by 2 because its only half a sphere

  15. anonymous
    • 5 years ago
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    what do you mean?

  16. dumbcow
    • 5 years ago
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    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

  17. anonymous
    • 5 years ago
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    i find the volume is 1152pi

  18. dumbcow
    • 5 years ago
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    correct

  19. anonymous
    • 5 years ago
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    SA is 432pi right?

  20. dumbcow
    • 5 years ago
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    no i get 288pi SA = 4pi*12^2 = 4pi*144 = 576pi take half of 576 288

  21. anonymous
    • 5 years ago
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    ok thank here the another question: The shaded circle at right has area 40π cm2. Find the surface area of the sphere.

  22. dumbcow
    • 5 years ago
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    i dont understand how are the circle and sphere related?

  23. anonymous
    • 5 years ago
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    here the hint:The surface area of a sphere is how many times the area of a circle with the same radius?

  24. dumbcow
    • 5 years ago
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    ok so they share the same radius is the entire circle shaded?

  25. anonymous
    • 5 years ago
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    here the picture

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  26. dumbcow
    • 5 years ago
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    ok thanks use area of circle formula to find radius, then plug that into SA formula A = pi*r^2 = 40pi

  27. anonymous
    • 5 years ago
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    i have to divide pi in both side

  28. dumbcow
    • 5 years ago
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    yes

  29. anonymous
    • 5 years ago
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    i find the raidus 6.32455532

  30. dumbcow
    • 5 years ago
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    correct

  31. dumbcow
    • 5 years ago
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    SA=4pi*(6.32)^2

  32. anonymous
    • 5 years ago
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    159.7pi

  33. dumbcow
    • 5 years ago
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    correct and you can round up to 160 since we rounded the radius

  34. anonymous
    • 5 years ago
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    Find the volume of a sphere whose surface area is 64π cm2.

  35. dumbcow
    • 5 years ago
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    first find radius 4pi*r^2 = 64pi

  36. anonymous
    • 5 years ago
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    4

  37. dumbcow
    • 5 years ago
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    good now use that to find volume V = 4/3pi*r^3

  38. anonymous
    • 5 years ago
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    i got 256pi over 3

  39. dumbcow
    • 5 years ago
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    correct

  40. anonymous
    • 5 years ago
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    Find the surface area of a sphere whose volume is 288π cm3.

  41. dumbcow
    • 5 years ago
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    same thing we just did except use volume formula to find radius V = 4/3pi*r^3 = 288pi

  42. anonymous
    • 5 years ago
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    what should i do with 4/3 pi?

  43. dumbcow
    • 5 years ago
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    well first get rid of pi by dividing pi on both sides like last time then we will divide by 4/3

  44. anonymous
    • 5 years ago
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    x by 3/4 by both side

  45. dumbcow
    • 5 years ago
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    correct

  46. anonymous
    • 5 years ago
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    what about 288*3/4

  47. dumbcow
    • 5 years ago
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    think of it as (288*3)/4

  48. anonymous
    • 5 years ago
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    i got 6 as radius

  49. dumbcow
    • 5 years ago
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    correct put that in SA formula

  50. anonymous
    • 5 years ago
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    144pi

  51. dumbcow
    • 5 years ago
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    correct

  52. anonymous
    • 5 years ago
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    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?

  53. anonymous
    • 5 years ago
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  54. dumbcow
    • 5 years ago
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    you can do this one, its just using the formula for circle area and SA the radius is just r

  55. anonymous
    • 5 years ago
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    ok i will but i need to leave right but i tell you when i get home

  56. dumbcow
    • 5 years ago
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    k

  57. anonymous
    • 5 years ago
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    ok i'm back so my homewprk paper has Agreat cicrle=,Shemisphere= and SA Hemisphere=__xA of great circle

  58. dumbcow
    • 5 years ago
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    yes lets fill in the gaps A = area circle SA = area circle + 1/2 SA of sphere

  59. anonymous
    • 5 years ago
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    the area of that is pir^2

  60. dumbcow
    • 5 years ago
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    good A = pir^2

  61. anonymous
    • 5 years ago
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    we know the radius is r so that mean..

  62. dumbcow
    • 5 years ago
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    whats SA of sphere

  63. anonymous
    • 5 years ago
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    4pir^2

  64. dumbcow
    • 5 years ago
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    good SA hemishere = pir^2 +(1/2)*4pir^2 add like terms

  65. anonymous
    • 5 years ago
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    3pir^2

  66. dumbcow
    • 5 years ago
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    good and A = pir^2 right? so SA = ___ * A

  67. anonymous
    • 5 years ago
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    what the of Agreat cicrle= and Shemisphere=

  68. anonymous
    • 5 years ago
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    i forgot to put answer

  69. dumbcow
    • 5 years ago
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    A = pir^2 SA hemishere = pir^2 +(1/2)*4pir^2 add like terms

  70. anonymous
    • 5 years ago
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    so that is the answer or i have to solve it

  71. dumbcow
    • 5 years ago
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    no thats the answer, remember we dont know what r is

  72. anonymous
    • 5 years ago
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    oh ok so SA = r * A

  73. dumbcow
    • 5 years ago
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    well does that sense? sub in what we know SA = 3pir^2 and A=pir^2 3pir^2 = r*pir^2 is that true?

  74. anonymous
    • 5 years ago
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    not really

  75. dumbcow
    • 5 years ago
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    ok look at it this way SA = 3pir^2 if i plug in A for pir^2 i get SA = 3A

  76. anonymous
    • 5 years ago
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    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?

  77. dumbcow
    • 5 years ago
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    ok use what we just learned SA = 3A = 4 gal + gal for the floor

  78. anonymous
    • 5 years ago
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    rid of a and 5 gal

  79. dumbcow
    • 5 years ago
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    sorry i was unclear there we dont know num of gall for the floor, lets call it x

  80. anonymous
    • 5 years ago
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    ok

  81. dumbcow
    • 5 years ago
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    we know SA of top is 2*pir^2 SA = 2pir^2 = 2A

  82. dumbcow
    • 5 years ago
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    2A = 4 gall

  83. anonymous
    • 5 years ago
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    then divide by 2

  84. anonymous
    • 5 years ago
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    A = 2 gal

  85. dumbcow
    • 5 years ago
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    yes

  86. dumbcow
    • 5 years ago
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    total = 3A A = 2 gall so total = 3*2 = 6 gallons

  87. anonymous
    • 5 years ago
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    i got it thank you so much

  88. dumbcow
    • 5 years ago
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    your welcome

  89. anonymous
    • 5 years ago
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    if i need help for my homework can u help me

  90. dumbcow
    • 5 years ago
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    yeah if you post it and im on sure

  91. anonymous
    • 5 years ago
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    thank again ^_^ that help me a lot from you

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