Parametric Surfaces and their Areas

dancingmonkey
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Homework Statement



Find the area of the part of the plane 3x + 5y + z = 15 that lies inside the cylinder x^2 + y^2 = 25.


Homework Equations



A=∫∫(√1+(dz/dx)^2+(dz/dy)^2) dA

The Attempt at a Solution


my bounds were r=0 to 5 and theta=0 to 2pi

∫∫√1 + (-3)^2 + (-5)^2 dA
=∫∫√35 dA


Is this right so far?
 
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It's right so far.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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