Help with solid of revolution volume question

[student93]

Homework Statement

The problem is attached in this post.

Homework Equations

The problem is attached in this post.

The Attempt at a Solution

I used washer method and set my outer radius as 2+2+√(x-1) and my inner radius as 2. I set my upper limit as 5 and my lower limit as 2.

I set my integral as π∫((4+√(x-1))^2-(4) dx, from 2 to 5 = 485π/6 which is incorrect, the actual answer is 157π/6.

 

[Saitama]

I used washer method and set my outer radius as 2+2+√(x-1)

Hi student93!

Why do you set the outer radius to 2+2+√(x-1)? Outer radius is simply 2+√(x-1), do you see why?

 

[student93]

Could you please explain why that's the value of the outer radius? Also is the value of my inner radius correct?

 

[Saitama]

Could you please explain why that's the value of the outer radius?

Draw a graph and select a disk, it becomes clear why the outer radius is that.

Also is the value of my inner radius correct?

Yes. :)