plotting a bivariate quadratic curve

Hi,

I would like to plot a x,y curve described by the equation :

Ax^2 + Bx + Cy^2 + Dy + E == 0

(A,B,C,D,E are constants)

This sounds like quite the common task but haven't been able to figure
out how to do this. Could you please help ? I am new to R so probably
missing something basic.

Thanks