f(x)=(x²+1)^1/2
f'(x) =1/2 (x²+1)^(-1/2) *2x=x*(x²+1)^(-1/2)
f''(x )= ...dupa calcule..=(x²+1)^(-3/2)
expresia devine
(x²+1)*1/(x²+1)^(3/2) +x* x/(x²+1)^1/2=
1/(x² +1)^1/2 +x²/(x²+1)^1/2=
(x²+1)/(x²+1)^1/2= (x²+1)^1/2= radical din (x²+1)
adevarat oricare x
