6.
若函数\(f(x)\)满足:对于任意正数\(s\),\(t\),都有\(f(s) > 0\),\(f(t) > 0\),且\(f(s)+f(t) < f(s+t)\),则称函数\(f(x)\)为“\(L\)函数”.
\((1)\)试判断函数\(f_{1}(x)=x^{2}\)与\(f_{2}(x)=x^{ \frac {1}{2}}\)是否是“\(L\)函数”;
\((2)\)若函数\(g(x)=3^{x}-1+a(3^{-x}-1)\)为“\(L\)函数”,求实数\(a\)的取值范围;
\((3)\)若函数\(f(x)\)为“\(L\)函数”,且\(f(1)=1\),求证:对任意\(x∈(2^{k-1},2^{k})(k∈N*)\),都有\(f(x)-f( \dfrac {1}{x}) > \dfrac {x}{2}- \dfrac {2}{x}\).