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anonymous

  • 5 years ago

Multiple choice: Can someone please please help me with some more surface area of pyramids and cones???

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  1. anonymous
    • 5 years ago
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  2. anonymous
    • 5 years ago
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    do you know the formula for finding out the surface area of a cone?

  3. anonymous
    • 5 years ago
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    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 \[\sqrt{r ^{2}+y ^{2}}\]

  4. anonymous
    • 5 years ago
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    all you need to do now is substitute the values of the radius and hypotenuse in the formula and you will have your answer

  5. anonymous
    • 5 years ago
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    i think its c, but i want a second opinion

  6. anonymous
    • 5 years ago
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    how did you get c?

  7. anonymous
    • 5 years ago
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    i did it but i lost the paper

  8. anonymous
    • 5 years ago
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    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 \[\sqrt{2^{2}+y ^{2}}\]

  9. anonymous
    • 5 years ago
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    where radius = 2

  10. anonymous
    • 5 years ago
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    \[138.23=12.56+6.28\times \sqrt{2^{2}+ y ^{2}}\]

  11. anonymous
    • 5 years ago
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    how would i solve for y

  12. anonymous
    • 5 years ago
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    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)

  13. anonymous
    • 5 years ago
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    so it would be b

  14. anonymous
    • 5 years ago
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    no, try again.

  15. anonymous
    • 5 years ago
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    nvm i thought we were solving for x

  16. anonymous
    • 5 years ago
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    you need to know the value of y to solve for x.

  17. anonymous
    • 5 years ago
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    because x = sqrt(r^2+y^2)

  18. anonymous
    • 5 years ago
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    y = sqrt((((138.23-12.56)/6.28)^2) - 4).. doing this i got 11.03

  19. anonymous
    • 5 years ago
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    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)

  20. anonymous
    • 5 years ago
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    19.9.. so e

  21. anonymous
    • 5 years ago
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    right, substituting x = sqrt(19.9^2+2^2) = sqrt(400.44) = 20.011 approximately

  22. anonymous
    • 5 years ago
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    thank you

  23. anonymous
    • 5 years ago
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    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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