найти 2 производную
y=ln(x+sqrt(1+x^2))
1 2x 1 (x+√(1+x²)) 1
y'=-------------- ·(1+-----------)= ------------ ·---------------- = -------- =(1+x²)^(-1/2)
(x+√(1+x²)) 2√(1+x²) x+√(1+x²) √(1+x²) √(1+x²)
(y' )' =[ (1+x²)^(-1/2) ]'= - (1/2)·(1+x²)^(-3/2)·2x=- x/((1+x²)^(3/2)=
-x
= ------------------
(1+x²)√(1+x²)