- by the different sign of the squares you can see that the graph of this relation must be a hyperbola.
- by the existence of a summand containing xy you can see that the axes of the hyperbola are not parallel to the x- and y-axis. (see attachment)
Unfortunately I haven' found a way to calculate the coordinates of the centre of the hyperbola (that's the point A in the attachment) and to calculate the equation of the axes (the equations of the axes are given with rounded coefficients: line a and b in the attachment)
If you could find the centre then you have to translate the centre to the origin and afterwards rotate the hyperbola counterclockwise.
I'm very sorry that I can't help you any further.