sammy12
A solid candy jawbreaker is cut in half. If its diameter is 4 cm, what is the surface area of a half piece? please show me the steps.
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beth1127
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|dw:1328844308091:dw|
sammy12
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i am getting 8 pi .is it right
Tonik
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i think it should be 48pi
Tonik
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oh hell, no.... i thought radius was 4, not diameter... sec
sammy12
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answer is 12 pi.I don't know how
funinabox
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2A = 4pi*r^2
2A = 4pi*(2)^2
2A = 16pi
A = 8pi
I set it equal to 2A because we want half the surface area, I found the full SA then divided by 2.
sammy12
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i am getting 8 pi
Tonik
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the surface area on the outside is 8pi, you're correct, but you need to add the surface are where the cut was made (basically the area of a circle radius 4
Tonik
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ugh, radius 2
Tonik
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so its 12pi
sammy12
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please can you explain
funinabox
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Ahhh yes I forgot about the inside cut. I assumed a hollow sphere. :O stupid mee
Xishem
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It's the surface area of half a sphere plus the surface area of the circle...
\[\frac{4πr^2}{2}+\pi r^2=2 \pi r^2+\pi r ^2=3 \pi r^2= 3 \pi (2cm)^2=12 \pi\ cm\]
Xishem
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*\[12\pi\ cm^2\]
sammy12
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Thanks