anonymous
  • anonymous
Multiple choice: Can someone please please help me with some more surface area of pyramids and cones???
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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katieb
  • katieb
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anonymous
  • anonymous
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anonymous
  • anonymous
do you know the formula for finding out the surface area of a cone?
anonymous
  • anonymous
if not, it is \[\pi (radius)^{2} + (\pi *radius* hypotenuse)\] In the given figure, the radius is denoted by r and the height of the cone is denoted by y. so, by pythogarus's theorem, the hypotenuse, denoted by x is \[\sqrt{r ^{2}+y ^{2}}\]

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anonymous
  • anonymous
all you need to do now is substitute the values of the radius and hypotenuse in the formula and you will have your answer
anonymous
  • anonymous
i think its c, but i want a second opinion
anonymous
  • anonymous
how did you get c?
anonymous
  • anonymous
i did it but i lost the paper
anonymous
  • anonymous
so, 138.23m^2 is the surface area. substituting in the formula, we get, \[138.23 = \pi*2^{2}+\pi*2*\sqrt{2^{2}+y ^{2}}\] solve for y. x will be \[\sqrt{2^{2}+y ^{2}}\]
anonymous
  • anonymous
where radius = 2
anonymous
  • anonymous
\[138.23=12.56+6.28\times \sqrt{2^{2}+ y ^{2}}\]
anonymous
  • anonymous
how would i solve for y
anonymous
  • anonymous
138.23=12.56+6.26(sqrt(4+y^2)) therefore 138.23-12.56 = 6.28(sqrt(4+y^2)) therefore (138.23-12.56)/6.28 = sqrt(4+y^2) therefore 4+y^2 = ((138.23-12.56)/6.28)^2 therefore y^2 = (((138.23-12.56)/6.28)^2) - 4 therefore y = sqrt((((138.23-12.56)/6.28)^2) - 4)
anonymous
  • anonymous
so it would be b
anonymous
  • anonymous
no, try again.
anonymous
  • anonymous
nvm i thought we were solving for x
anonymous
  • anonymous
you need to know the value of y to solve for x.
anonymous
  • anonymous
because x = sqrt(r^2+y^2)
anonymous
  • anonymous
y = sqrt((((138.23-12.56)/6.28)^2) - 4).. doing this i got 11.03
anonymous
  • anonymous
lets take this one step at a time: 138.23-12.56 = 125.67 125.67/6.28 = 20.011 20.011^2 = 400.44 400.44-4 = 396.44 y = sqrt(396.44)
anonymous
  • anonymous
19.9.. so e
anonymous
  • anonymous
right, substituting x = sqrt(19.9^2+2^2) = sqrt(400.44) = 20.011 approximately
anonymous
  • anonymous
thank you
anonymous
  • anonymous
you are welcome. It is really easy once you know the formula. it is all a matter of substituting the correct values.

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