$$\{(x,y)\,|\,Ax+By+Cz=0\} = L$$ \begin{flushright}\dag \end{flushright}[1]
I am trying to align the dagger so it is flushed to the right but on the same line as the equation. When i insert \begin{flushright}\dag \end{flushright}inside $$ I get a compiling error.

\[ ... \]preferable to$$ ... $$for why one shouldn't use$$in a LaTeX document to initiate and terminate display-math mode. – Mico Jan 26 '20 at 15:36