2.
.已知函数\(f\)\((\)\(x\)\()\)是定义在\((0,\)\(+\)\(∞\)\()\)上的单调函数,且对任意的正数\(x\),\(y\)都有\(f\)\((\)\(xy\)\()\)\(=f\)\((\)\(x\)\()\)\(+f\)\((\)\(y\)\()\).若数列\(\{\)\(a_{n}\)\(\}\)的前\(n\)项和为\(S_{n}\),且满足\(f\)\((\)\(S_{n}+\)\(2)\)\(-f\)\((\)\(a_{n}\)\()\)\(=f\)\((3)(\)\(n\)\(∈N\)\({\,\!}^{*}\)\()\),则\(a_{n}\)等于\((\) \()\)