The attached picture skips a lot of the work, but I've worked this problem at least 6 times in the last 8 hours, still getting stuck at reducing to canonical form - that is, trying to solve for $x$ and $y$ within the system of equations. I cannot determine how to solve for $x$ and $y$ in terms of $\xi$ and $\eta$. Is there some trick I'm not seeing or some better choice of $\eta$? The equation is supposed to be solvable.
