LaTeX.org

Hi everyone,

I'm new to LaTeX and I'm trying to plot an ellipsis given by the function:
x^2+a*xy+y^2=1, where a is element of the real numbers.
I'm not quite sure what's the best way to this, I thought of using the tikZ package, but I'm only know how to plot simple functions, e.g. f(x)=x^2.

Would ...