# Toronto Math Forum

## APM346-2016F => APM346--Lectures => Chapter 8 => Topic started by: Shentao YANG on November 13, 2016, 01:20:23 PM

Title: HA9, Problem6
Post by: Shentao YANG on November 13, 2016, 01:20:23 PM

Can any explain in detail the reason behind the hint "solution must be a harmonic polynomial of degree $3$ and it should depend only on $x^2+y^2+z^2$ and $z$"?
Concretely, there are $3$ question need to be addressed:
$(1)$ Why the solution need to be a harmonic polynomial?
$(2)$ Why it should have degree $3$?
$(3)$ Why it should depend only on $x^2+y^2+z^2$ and $z$ but not the other terms?
The solution from the previous year basically made no reasonable explanation and just copied words from the textbook

http://forum.math.toronto.edu/index.php?topic=731.0
Title: Re: HA9, Problem6
Post by: Victor Ivrii on November 15, 2016, 07:06:04 AM
Consider it as a Hint. We have not finished harmonic polynomials on the lecture.
Also, since problem depends only on $x^2+y^2$ and $z$ (is invariant with respect to rotations around $z$ axis), so does the solution