Region bounded by $y= x$, $x=0$ and $y=15$, rotated about the x-axis and y-axis

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I am wondering if there is a difference between the answers of these when getting the volume of solid of revolution:

Region bounded by $y = x$, $x = 0$ and $y = 15$, rotated about the $x-axis$

Region bounded by $y = x$, $x = 0$ and $y = 15$, rotated about the $y-axis$

I tried the first one which is rotated about the x-axis and I got $2250π$.

For the second one I am confused on how to solve, is it possible that I use any of disk, washer, or shell method?

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No objects are not the same.

  • Your region is the following triangle:

enter image description here


  • Rotation around the $x$-axis:

enter image description here


  • Rotation around the $y$-axis:

enter image description here


However, you should be able to see the relation between their volumes.

0
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Volume of the figure produced by rotation is equal to $V = 2 *S * π * r$

Where S is area of cross-section, r is distance of the center of mass from rotation axis.

For x it is 10, for y it is 5, see pic.

So we get for the first case $2 *1/2 * 15^2 * 10 = 2250 π$ In second case $2 *1/2 * 15^2 * 5 = 1125 π$

plot of the area

enter image description here