1.
设\(A({{x}_{1}},f\left( {{x}_{1}} \right))\),\(B({{x}_{2}},f\left( {{x}_{2}} \right))\)是函数\(f\left( x \right)=\dfrac{1}{2}+{{\log }_{2}}\left( \dfrac{x}{1-x} \right)\)的图象上的任意两点.
\((1)\)当\({{x}_{1}}+{{x}_{2}}=1\)时,求\(f\left( {{x}_{1}} \right)+f\left( {{x}_{2}} \right)\)的值;
\((2)\)设\({{S}_{n}}=f\left( \dfrac{1}{n+1} \right)+f\left( \dfrac{2}{n+1} \right)+f\left( \dfrac{3}{n+1} \right)+\cdots \cdots f\left( \dfrac{n-1}{n+1} \right)+f\left( \dfrac{n}{n+1} \right)\),其中\(n\in {{N}^{*}}\),求\({{S}_{n}}\);
\((3)\)对应\((2)\)中\({{S}_{n}}\),已知\({{a}_{n}}={{\left( \dfrac{1}{{{S}_{n}}+1} \right)}^{2}}\),其中\(n\in {{N}^{*}}\),设\({{T}_{n}}\)为数列\(\left\{ {{a}_{n}} \right\}\)的前\(n\)项和,求证\(\dfrac{4}{9}\leqslant {{T}_{n}} < \dfrac{5}{3}\).