y=In(x+√(x^2-a^2),
y'=(1+x/√(x^2-a^2)/[x+√(x^2-a^2)]
y=x√(1-x^2)+arcsinx
y'=√(1-x^2)-x^2/√(1-x^2)+1/√(1-x^2)=2√(1-x^2)