9.
已知函数\(f(x)={\log }_{2}x,x∈[2,8] \),函数\(g\left( x \right)={{\left[ f\left( x \right) \right]}^{2}}-2a\cdot f\left( x \right)+3\)的最小值为\(h\left( a \right)\).
\((\)Ⅰ\()\)求\(h\left( a \right)\);
\((\)Ⅱ\()\)是否存在实数\(m\),\(n\),同时满足以下条件:\(①m > n > 3\);\(②\)当\(h\left( a \right)\)的定义域为\([n,m]\)时,值域为\([{n}^{2},{m}^{2}] .\)若存在,求出\(m\),\(n\)的值;若不存在,说明理由.