$x_0>0$x_0>0 i $y_0>0$y_0>0

$x_0>0$x_0>0 i $y_0<0$y_0<0

$x_0<0$x_0<0 i $y_0>0$y_0>0

$x_0<0$x_0<0 i $y_0<0$y_0<0