Let f: X be differentiable at x and g: Y be differentiable at y with f(y) 0. Then their quotient f/g: X Ã Y is

Let f: X †’ „œ be differentiable at x and g: Y †’ „œ be differentiable at y with f(y) ‰  0. Then their quotient f/g: X × Y †’ „œ is differentiable at (x, y) with derivative

g(y)Df x-f(x)Dg|y] (g(y))? D-x, y)