I am new and I have one new question :)
i am trying these question, i must to show:
except at (a,b)
I differentiated twice for z and for x (chain rule and quotient) and put in equation to get:
I think it is ok and it does not work for a, b (as it goes to infinity) but is it enough to do this and say equation is satisfied? sorry if is obvious question! or have i done calculation wrong?