Volume of Revolution: Find the Volume from y = x+6 & y = x^2 - 4x

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Homework Statement


The line y = x + 6 meets the curve y = x2-4x at the points P and Q. Find the volume of the solid generated when the area enclosed by the line and the curve is rotated through 360o about the x-axis


Homework Equations


Integration


The Attempt at a Solution


I've drawn the graph and found the intersections, which are x = -1 and x = 6. The region are located in first, second, and fourth quadrants. I'm confused about the region in fourth quadrant.
How to find the volume of all the region when they are rotated 360o about the x-axis? I can't imagine what shape it forms, I think the region in fourth quadrant will "overlap" with region in first quadrant when rotated.

Thanks
 
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hi songoku! :smile:

yes, you're right … that doesn't make sense :redface:

is that the whole question? I'm wondering why they bothered to give points P and Q names :confused:
 
tiny-tim said:
hi songoku! :smile:

yes, you're right … that doesn't make sense :redface:

is that the whole question? I'm wondering why they bothered to give points P and Q names :confused:

hi tiny-tim! :smile:

Yes, that's the whole question. I just noticed that we don't need P and Q, just say "the area enclosed by the line and the curve" is enough.

For now, let's assume there is mistake in the question :biggrin:

Thanks tiny-tim!
 
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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