3.
\((1)\)已知各项均为正数的等比数列\(\{a_{n}\}\)满足\(a_{7}=a_{6}+2a_{5}\),若存在两项\(a_{m}\),\(a_{n}\)使得\( \sqrt{a_{m}a_{n}}=4a_{1}\),则\( \dfrac{1}{m}+ \dfrac{4}{n}\)的最小值为_____________.
\((2)S_{n}\)为数列\(\{a_{n}\}\)的前\(n\)项和\(.\)已知\(a_{n} > 0\),\(a\rlap{_{n}}{^{2}}+2a_{n}=4S_{n}+3\).
\(①\)求\(\{a_{n}\}\)的通项公式;
\(②\)设\(b_{n}= \dfrac{1}{a_{n}a_{n+1}}\),求数列\(\{b_{n}\}\)的前\(n\)项和.