Question

va rog, punctul b)! Mulțumesc!​

Answer 1

$\it -2<\dfrac{4x}{x^2+1}<2|_{:2} \Rightarrow -1<\dfrac{2x}{x^2+1}<1|_{\cdot (x^2+1)} \Rightarrow \\ \\ \\ \Rightarrow-x^2-1 < 2x <x^2+1}|_{-2x} \Rightarrow -(x^2+2x+1)<0<x^2+x+1 \Rightarrow \\ \\ \\ \Rightarrow -(x+1)^2<0<(x+1)^2\ \ (A)$