Z = arcsin (XY) to find the second derivative of this function There are four answers, two of which are equal

Z = arcsin (XY) to find the second derivative of this function There are four answers, two of which are equal

z'x=y/√(1-x^2y^2)
z'y=x/√(1-x^2y^2)
z"xx=y*(-1/2)*(1-x^2y^2)^(-3/2)*(-2xy^2)=xy^3*(1-x^2y^2)^(-3/2)
z"xy=z"yx=[√(1-x^2y^2)-y*(-2x^2y)/2√(1-x^2y^2)]/(1-x^2y^2)=(1-x^2y^2)^(-3/2)
z"yy=x*(-1/2)*(1-x^2y^2)^(-3/2)*(-2x^2y)=x^3y(1-x^2y^2)^(-3/2)