9.
\((1)\)若\(∫_{1}^{a}\left(2x+ \dfrac{1}{x}\right)dx=3+\ln 2\left(a > 1\right) \),则\(a\)的值是___________.
\((2)\)有\(6\)名学生,其中有\(3\)名会唱歌,\(2\)名会跳舞,\(1\)名既会唱歌也会跳舞\(.\)现从中选出\(2\)名会唱歌的,\(1\)名会跳舞的去参加文艺演出,则共有选法______种.
\((3)\)在矩形\(ABCD \)中,对角线\(AC \)与相邻两边所成角分别为\(α \),\(β \),则有\({\cos }^{2}a+{\cos }^{2}β=1 \),类比到空间中的一个正确命题是:在长方体\(ABCD-{A}_{1}{B}_{1}{C}_{1}{D}_{1} \)中,对角线\(A{C}_{1} \)与相邻三个面所成角分别为\(α \),\(β \),\(γ \),则有\({\cos }^{2}a+{\cos }^{2}β+co{s}^{2}γ= \) .
\((4)\)如图,\(A\),\(B\)为抛物线\({y}^{2}=4x \)上的两点,\(F\)为抛物线的焦点且\(FA⊥FB \),\(C\)为直线\(AB\)上一点且横坐标为\(-1\),连结\(FC.\)若\(\left|BF\right|=3\left|AF\right| \),则\(\tan c= \) ______.