Răspuns :
f(x) = ln[(1-x)/(1+x)] = ln(1-x) - ln(1+x)
f'(x) = -1/(1-x) - 1/(1+x) = -(x+1+1-x)/[(1-x)(1+x)] =
= -2/[(1-x)(1+x)]
f'(x) = -1/(1-x) - 1/(1+x) = -(x+1+1-x)/[(1-x)(1+x)] =
= -2/[(1-x)(1+x)]