> with(DEtools):
> eqn:=diff(y(x),x)=sqrt(1-y(x)^2);
                                                   (1/2)
                              d         /        2\     
                      eqn := --- y(x) = \1 - y(x) /     
                              dx                        
> DEplot(eqn,y(x),x=-2..2, y=-1..1);

> dsolve({eqn,y(0)=0},y(x));
                                y(x) = sin(x)
> DEplot(eqn,y(x),x=-4..2, y=-1..1, {[y(0)=0]},linecolor=black,stepsize=0.1);

> dsolve({eqn,y(0)=1},y(x));
                                   y(x) = 1
> DEplot(eqn,y(x),x=-4..2, y=-1..1, {[y(0)=1]},linecolor=black,stepsize=0.1);

>