The equation $ax^2$ + 2hxy + $by^2$ + 2gx + 2fy + c = 0 represents a pair of lines when Delta = abc + 2fgh - $af^2$ - $bg^2$ - $ch^2$ = 0. The point of intersection is found by solving partial derivatives: ax + hy + g = 0 and hx + by + f = 0. The angle between the lines is the same formula as the homogeneous case: tan(theta) = 2*sqrt($h^2$ - ab)/|a + b|.