Show that the following limits do not exist:

$(x,y)(1,2)\underset{?}{lim}\frac{xY-2x-Y+2}{x^2+Y^2-2x-4Y+5}$

$\underset{(x,y)(0,0)}{lim}\frac{x^{2}Y}{x^4+Y^2}$

Find the partial derivatives: