Moment of inertia, double integral

[Feodalherren]

Homework Statement

Homework Equations

The Attempt at a Solution

For part B, why is he using the formula for the moment of inertia about the y-axis? Why isn't he using the formula for the moment of inertia about the origin?

http://www.math24.net/physical-applications-of-double-integrals.html

The formula that I'm referring to is the "polar moment of inertia" in this list.

 

[maajdl]

We can't read any problem statement and relevant equations in you post.
What's the question?

Note that a moment of inertia is always defined with respect to an axis (of rotation).
There is nothing like a moment of inertia about a point like the origin.

 

[Feodalherren]

You can't see the picture? I can see it :/.

The formulas are in the link.
I don't know what to tell you. The problem is asking for moment of inertia about the origin. The list of integrals also has a formula for "polar moment of inertia".