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carlodelmundo
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Homework Statement
A manufacturer drills a hole through the center of a metal sphere of radius 5 inches. The hole has a radius of 3 inches. What is the volume of the resulting metal ring?
Solution:
You can imagine the ring to be generated by a segment of the circle who equation is x^2 + y^2 = 25. Because the radius of the hole is 3 inches, you can let y = 3 and solve the equation x^2 + y^2 = 25 to determine that the limits of integration are x = +- 4 . So, the inner and outer radii are r(x) = 3 and R(x) = sqrt(25-x^2).
Homework Equations
x^2 + y^2 = r^2 (Standard Form of A Circle)
The Attempt at a Solution
This is an example problem in my textbook, Calculus 8th Edition by Larson (pg. 461 Section 7.2)
My fundamental question: How did they find the limits of integration by substituting 3 with y?
I just don't see how plugging in the inner radius (y = 3) into the equation of a circle would find the limits of integration? I can see how in a 2D circle, x has solutions when it is -4 and 4...but why couldn't we plug in radius (y = 5) in instead of 3?
Thanks