2.
\((1)\)已知\(\sin α= \dfrac{3}{5}\),\(α∈( \dfrac{π}{2},π)\),则\(\cos \alpha =\)________,\( \dfrac{\cos 2α}{ \sqrt{2}\sin (α+ \dfrac{π}{4})}=\)________.
\((2)\)已知数列\(\{a_{n}\}\)的首项为\(1\),数列\(\{b_{n}\}\)为等比数列且\(b_{n}= \dfrac{a_{n+1}}{a_{n}}\),若\(b_{10}·b=2\),则\({{b}_{7}}{{b}_{14}}=\)_____,\(a_{21}=\)________.
\((3)\)计算:\(\tan 20^{\circ}+\tan 40^{\circ}+ \sqrt{3}\tan 20^{\circ}\tan 40^{\circ}=\)________,\( \dfrac{ \sqrt{3}\tan 12^{\circ}-3}{(4\cos ^{2}12^{\circ}-2)\sin 12^{\circ}}=\)________.
\((4)\)数列\(\left\{ {{a}_{n}} \right\}\)满足\({{a}_{1}}=1\),\(\sqrt{\dfrac{1}{{{a}_{n}}^{2}}+2}=\dfrac{1}{{{a}_{n+1}}}\left( n\in {{N}^{*}} \right)\),记\({{b}_{n}}={{a}_{n}}^{2}\),则数列\(\left\{ {{a}_{n}} \right\}\)的通项公式\({{a}_{n}}=\)____________,数列\(\left\{ {{b}_{n}}{{b}_{n+1}} \right\}\)前\(n\)项和\({{S}_{n}}=\)___________.
\((5)\)在\(200 m\)高的山顶上,测得山下一塔顶与塔底的俯角分别为\(30^{\circ}\)与\(60^{\circ}\),则塔高是_____\(m\).
\((6)\)若\(\sin \alpha +\sin \beta =\dfrac{\sqrt{2}}{2},\)则\(\cos \alpha +\cos \beta \)的取值范围_____.
\((7)\)设数列\({{a}_{n}}\)满足:\({{a}_{1}}=\sqrt{3}\),\({{a}_{n+1}}=\left[ {{a}_{n}} \right]+\dfrac{1}{\left\{ {{a}_{n}} \right\}}\),其中,\(\left[ {{a}_{n}} \right]\)、\(\left\{ a{}_{n} \right\}\)分别表示正数\({{a}_{n}}\)的整数部分、小数部分,则\({{a}_{2018}}=\)_____.