6.
\((1)\)已知实数\(a > 0\),\(b > 0\),
,则\(\dfrac{1}{a}+ \dfrac{2}{b} \)的最小值是______.
\((2)\)已知数列\(\{a_{n}\}\)的前\(n\)项和为\(S_{n}\),且\(S_{n}=n^{2}+1\),则 \(a_{n=\_\_\_\_\_\_\_\_\_\_\_\_\_}\)
\((3)\)如图所示,在正方体\(ABCD-A_{1}B_{1}C_{1}D_{1}\)中,\(M\),\(N\)分别为棱\(C_{1}D_{1}\),\(C_{1}C\)的中点,有以下四个结论:
\(①\)直线\(AM\)与\(CC_{1}\)是相交直线\(;②\)直线\(AM\)与\(BN\)是平行直线\(;\)
\(③\)直线\(BN\)与\(MB_{1}\)是异面直线\(; ④\)直线\(MN\)与\(AC\)所成的角为\(60^{\circ}\).
其中正确的结论为___ \((\)注:把你认为正确的结论序号都填上\().\)
\((4)\)若当\(x∈[1,3]\),\(y∈[2,4]\)时,\(\dfrac{a{{x}^{2}}+2{{y}^{2}}}{xy}-1 > 0\)恒成立,则\(a\)的取值范围是______