Setting up a triple integral in cylindrical coordinates?

AI Thread Summary
To find the volume of the material cut from the solid sphere defined by r^2 + z^2 ≤ 9 by the cylinder r = 3sin(θ), one must convert the equations to cylindrical coordinates. The sphere represents a volume with a radius of 3 centered at the origin, while the cylinder runs parallel to the z-axis. The limits for the triple integral are established as ∫ from 0 to 2π, ∫ from 0 to 3sin(θ), and ∫ from -√(9 - r^2) to √(9 - r^2). The conversion to cylindrical coordinates is confirmed as correct, with the integral set up appropriately for the problem. Understanding these transformations is crucial for accurately calculating the volume.
VinnyCee
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The problem says to find the volume of material cut from the solid sphere,

r^2 + z^2 \le 9

by the cylinder,

r = 3\sin\theta

I don't know how to graph the first equation, but I can do the second in polar coordinates. How do I go about converting to use cylindrical coordinates?
 
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VinnyCee said:
I don't know how to graph the first equation

It's a sphere of radius 3 centered at the origin:

r^2+z^2=x^2+y^2+z^2=9


but I can do the second in polar coordinates. How do I go about converting to use cylindrical coordinates?

It's already in cylindrical coordinates. The equation is implying that r=3sin(\theta) for all z.
 
I did a crude sketch and came up with this integral

Is this correct limits for the problem?

\int_{0}^{2\pi}\int_{0}^{3\sin\theta}\int_{-\sqrt{9 - r^2}}^{\sqrt{9 - r^2}}\;dz\;r\;dr\;d\theta
 
"Cylindrical coordinates" is simply polar coordinates with "z" added.
r= 3 sin \theta, a circle with center at (0, 3/2), radius 3/2, in polar coordinates is a cylinder running parallel to the z axis in cylindrical coordinates.
Since r2= x2+ y2, the sphere, x2+ y2+ z2= 9 is r2+ z2= 9 in cylindrical coordinates.
 
Looks good to me.
 
Many Thanks

Thank you both. When I have more time on my hands, I will be sure and return the favor to someone here someday :smile:
 
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