y=arcsin((2x)/(1+x^2))
(arcsinf(x))`=f`(x)/sqrt(1-f^2(x))
(2x/(1+x^2))`=((2x)`*(1+x^2)-(1+x^2)`*(2x))/(1+x^2)^2=
=(2+2x^2-4x^2)/(1+x^2)^2=2*(1-x^2)/(1+x^2)^2
О т в е т. 2*(1-x^2)/(1+x^2)^2/sqrt(1-(2x/(1+x^2))^2)=
=2*(1-x^2)/((1+x^2)*sqrt((1+x^2-2x)(1+x^2+2x)))=
=2*(1-x^2)/((1+x^2)*|1-x|*|1+x|)