Shell method - need help: rotate region enclosed by y = x^3 + x + 1, y = 1, x = 1 about x = 2

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engd

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Hi,
I am learning Calculus, and in one exercise I am not sur with a number -1 as you can see in the screen shot.
He added -1 because y=1 ?
Thank you in advance :)
 

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engd said:
Hi,
I am learning Calculus, and in one exercise I am not sur with a number -1 as you can see in the screen shot.
He added -1 because y=1 ?
Thank you in advance :)
Click to expand...
To be specific, he is not adding -1; he is subtracting the y-coordinate at the bottom, 1, from the y-coordinate at the top, [imath]x^3+x+1[/imath], to get the height, [imath]x^3+x+1-1=x^3+x[/imath].
 
Thank you Dr.Peterson,
If y was eguale 2 for example , I have to subtract -2 ?
 
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