# Can I say \$ iint f (x, y) dx dy = int f (x) dx cdot int f (y) dy \$ usually? ….

I can say that $$iint f (x, y) dx dy = int f (x) dx cdot int f (y) dy$$ usually ? Is it permissible to divide the integral in that way? And we know that integtal is linear. $$int f (x) + g (x) dx = int f (x) dx + int g (x) dx$$ I think this is not possible for $$iint f (x) + g (x) dx = int f (x) dx + int g (x) dx$$ straight ? On top of that, why is it $$iint f (x) g (y) dx dy = int f (x) dx int g (y) dy$$