Найдите производную второго порядка Y=√(1+x^2)*arctg x

====================================================================
Y= (x^2 +1 ) * arctg x
y' = x^2 + 1 * 1/ x^2 + 1 + 2x * arctg x = 1 + 2x * arctg x
====================================================================

y'=x arctg(x)/√(x^2 + 1) + 1/√(x^2 + 1)

y''=arctg(x)/(x^2 + 1)^(3/2)