6.
\((1)\)已知角\(α \)的终边经过点\(N\left(-3,4\right) \),则\(\cos α \)的值为_______________.
\((2)\)已知点\(P \)在线段\(AB \)上,且\(\left| \overset{→}{AB}\right|=4\left| \overset{→}{AP}\right| \),设\( \overset{→}{AP}=λ \overset{→}{PB} \),则实数\(λ= \) .
\((3)\)已知直三棱柱\(ABC-{A}_{1}{B}_{1}{C}_{1} \)的\(6\)个顶点都在球\(O \)的球面上,若\(AB=3,AC=4,AB⊥AC,A{A}_{1}=12 \),则球\(O \)的半径为______________.
\((4)\)点\(A\left(0,2\right) \)是圆\(Q:{x}^{2}+{y}^{2}=16 \)内定点,\(B,C \)是这个圆上的两动点,若\(BA⊥CA \),求\(BC \)中点\(M \)的轨迹方程为 .