e) Express dy in terms of x and dx if \sqrt{x} + \sqrt{y} = 1

So the first step is:

(1/2\sqrt{x})dx+(1/2\sqrt{y})dy=0

it says that the step above is implied. I don't understand really what is meant by the above or how the equation got into that form. I was able to do a)-d) no problem but the implied form of e) I don't understand. Maybe someone will explain?

Thank you...