Approximating surface area of hemisphere

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SUMMARY

The discussion focuses on approximating the surface area of a hemisphere using cylindrical segments. The user attempts to calculate the surface area by integrating the curved surface area of cylinders with a height of r.cos(theta) and a radius of r.sin(theta). However, the integration approach leads to an incorrect result of -pi r^2, indicating a fundamental misunderstanding of the approximation method. The conversation highlights the need for a more accurate integration technique to compute the surface area without resorting to volume methods.

PREREQUISITES
  • Understanding of integral calculus, specifically surface area calculations.
  • Familiarity with cylindrical coordinates and their application in geometry.
  • Knowledge of trigonometric functions, particularly sine and cosine.
  • Basic concepts of approximation methods in calculus.
NEXT STEPS
  • Study the derivation of the surface area formula for a hemisphere.
  • Learn about the method of cylindrical shells in calculus.
  • Explore the use of parametric equations in surface area calculations.
  • Investigate alternative approximation techniques for surface area beyond cylindrical segments.
USEFUL FOR

Students studying calculus, particularly those focusing on geometry and surface area, as well as educators seeking to clarify integration techniques for approximating geometric shapes.

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Homework Statement



i am trying to apprixmate the surface area of a hemisphere.
i am approximating by cutting the sphere into cylinders of different radius, and using their curved surface area to approximate.

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each cylinder will have a height of r.cos.theta and radius of r.sin.theta.

so the surface area should be =
integral [pi/2 to 0] (2.pi * r.sin.theta * r.cos.theta * d.theta)??

but that gives me -pi r^2 which is wrong...

anyidea where i went wrong?
 
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That's not going to work. Those cylnders do NOT approximate the surface area. The problem is exactly the same as if you used short vertical and horizontal segments to approximate the line from (0, 0) to (1, 1). They will always have a total length of 2 while the length of the the line is \sqrt{2}.
 
sorry i don't get you. can you elaborate?
how else can i integrate something to get the S.A.?
(without going through the volume method)
 

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