\( \Rightarrow \)\({x^2} + 1 = {(a - x)^2} = {x^2} - 2ax + {a^2}\)
\( \Rightarrow \)\(x = {{1 - {a^2}} \over { - 2a}} = {{{a^2} - 1} \over {2a}} = {1 \over 2}\left( {a - {1 \over a}} \right)\).