Hydrogen atom expectation of r^2 check

[keith river]

I haven't posted any of my working for this as I only want to check my answer.

Q. For a hydrogen atom with n=2, l=1, m=0
calculate <r^2>

My answer = 0.75 * a^2

where a is the bhor radius.

Am I right?

 

[ideasrule]

I don't think that's correct; I get a much larger answer. Can you show your work?