Question

$xdx-\sqrt{1-x^2}dy=0$

Answer 1

$\displaystyle x*dx=\sqrt{1-x^2}*dy\\\\\frac{x}{\sqrt{1-x^2}}*dx=dy\\\\\int \frac{x}{\sqrt{1-x^2}}dx=\int 1*dy\\\\ 1-x^2=t; -2xdx=dt; xdx=-dt/2\\\\-\frac{1}{2} \int \frac{1}{\sqrt{t}}dt=y\\\\-\frac{1}{2}*2\sqrt{t}+C=y\\\\-\sqrt{t}+C=y\\\\y=-\sqrt{1-x^2}+C$