u=arcsin(x/y)
y=√(x^2+1) dy/dx=2x*(1/2)/√(x^2+1)=x/√(x^2+1)
dx/dy=√(x^2+1)/x
d(x/y)/dy=(dx/dy)/y-x/y^2
=[√(x^2+1)/x ] /√(x^2+1) -x/y^2
=1/x-x/y^2
du/d(x/y)=1/√1-(x/y)^2=y/√(y^2-x^2)=y
du/dy=du/d(x/y)* d(x/y)/dy
=y*[1/x-x/y^2]=y/x-x/y
y=√(x^2+1) x=√(y^2-1)或 x=-√(y^2-1)
du/dy= y/√(y^2-1) -√(y^2-1)/y 或 du/dy= -y/√(y^2-1) +√(y^2-1)/y