I've got this question : Given $x^2 + y^2 − 2x + 4y = −9$, find $y'$. (I found $y' = -(x+1)/(y+2)$.
But then, it asks: Show that the result is nonsense. (Hint: appeal to the conditions of the implicit function theorem.)
I don't understand how I can do this. Could anyone help?
Hint: $x^2 + y^2 - 2x + 4y = (x-1)^2 + (y+2)^2 - 5$. Can this expression become equal to $-9$?