why is my disk volume method equation wrong? (integration)

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The volume of a solid obtained by rotating the region enclosed by:

y=1/x^4, y = 0, x = 1, and x = 8 

about the line y=-1 can be computed using the method of disks or washers via an integral...

The question is asking about the function and not the actual volume

I understand that it's a modification of the (pi)r^2dx idea and I got this:

pi(1+(1/x^4))^2

yet the place where I'm trying to submit this won't accept it. What am I doing wrong?

(Ignore the bounds I already have them listed as 1 to 8)