Răspuns:
Explicație pas cu pas:
f(x) = (x²-1)/(x²+1)
x²-1 = (x-1)(x+1)
x²+1 > 0 ; (∀) x ∈ R =>
x I -∞ -1 1 +∞
x-1 I-------------------0+++++++
x+1 I------------0+++++++++++
x²-1 I+++++++0------0++++++
x²+1 I +++++++++++++++++++
f(x) I+++++++0------0++++++