7.
已知函数\(f\left( x \right)=\dfrac{{lo}{{{g}}_{3}}\left( x+1 \right)}{x+1}\left( x > 0 \right)\)的图象上有一点列\({{P}_{n}}\left( {{x}_{n}},{{y}_{n}} \right)\left( n\in {{N}^{*}} \right)\),点\({{P}_{n}}\)在\(x\)轴上的射影是\({{Q}_{n}}\left( {{x}_{n}},0 \right)\),且\({{x}_{n}}=3{{x}_{n-1}}+2\) \((n\geqslant 2\)且\(n\in {{N}^{*}})\),\({{x}_{1}}=2\).
\((1)\)求证:\(\left\{ {{x}_{n}}+1 \right\}\)是等比数列,并求出数列\(\left\{ {{x}_{n}} \right\}\)的通项公式;
\((2)\)对任意的正整数\(n\),当\(m\in \left[ -1,1 \right]\)时,不等式\(3{{t}^{2}}-6mt+\dfrac{1}{3} > {{y}_{n}}\)恒成立,求实数\(t\)的取值范围.
\((3)\)设四边形\({{P}_{n}}{{Q}_{n}}{{Q}_{n+1}}{{P}_{n+1}}\)的面积是\({{S}_{n}}\),求证:\(\dfrac{1}{{{S}_{1}}}+\dfrac{1}{2{{S}_{2}}}+\ldots +\dfrac{1}{n{{S}_{n}}} < 3\).