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

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SUMMARY

The discussion focuses on calculating the volume of revolution generated by rotating the area enclosed by the line y = x + 6 and the curve y = x^2 - 4x about the x-axis. The intersection points of the line and curve are identified as x = -1 and x = 6. Participants express confusion regarding the fourth quadrant's contribution to the volume and the necessity of naming the intersection points P and Q. Ultimately, it is concluded that the area enclosed by the line and curve suffices for the volume calculation without needing to reference the intersection points.

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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!
 

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