z=x*arcsin[sqrt(x/y)]
dz/dy=x*1/sqrt(1-[sqrt(x/y)]^2)*(sqrt(x/y))'=x*1/sqrt(1-[sqrt(x/y)]^2)*(sqrt(x)/sqrt(y))'=
=x*1/sqrt(1-[sqrt(x/y)]^2)*sqrt(x)*(1/sqrt(y))'=x*1/sqrt(1-[sqrt(x/y)]^2)*sqrt(x)*(y^(-1/2))'=...