$
\eqalign{
& f(x) = \ln \left( {\frac{{1 + x}}
{{1 - x}}} \right) \cr
& f'(x) = \frac{1}
{{\frac{{1 + x}}
{{1 - x}}}} \cdot \left[ {\frac{{1 + x}}
{{1 - x}}} \right]^| \cr
& f'(x) = \frac{{1 - x}}
{{1 + x}} \cdot \frac{{1 \cdot \left( {1 - x} \right) - \left\{ {\left( {1 + x} \right) \cdot - 1} \right\}}}
{{\left( {1 - x} \right)^2 }} \cr
& f'(x) = \frac{{1 - x}}
{{1 + x}} \cdot \frac{{1 - x + 1 + x}}
{{\left( {1 - x} \right)^2 }} \cr
& f'(x) = \frac{1}
{{1 + x}} \cdot \frac{2}
{{1 - x}} = \frac{2}
{{\left( {1 + x} \right)\left( {1 - x} \right)}} \cr}
$