Simple question: Why the below formula is right?(I want to know the proof)
The equivalent in 2D geometry is $$ \nabla^2 \ln \mid\vec\theta-\vec\theta'\mid = 2\pi\delta^2(\vec\theta-\vec\theta')\ ,$$ where $\delta^2$ is the 2D delta function.
Because I wondered above, I asked to stack exchange in astronomy, So I get the link which explains it(stack exchange in math1, stack exchange in math2)
But my major is not mathematics, so it is hard to understand.
Is it impossible to understand by using only the basic knowledge of mathematics? I know only basic calculus(from James Stewart's book) and some basic linear algebra.
There is no context related to this proof in the stack exchange, you tube, or any other website.