2.
\((1)\)已知\(a\)与\(b\)为两个不共线的单位向量,\(k\)为实数,若向量\(a+b\)与向量\(ka-b\)垂直,则\(k=\)_____________.
\((2)\)若变量\(x\),\(y\)满足约束条件\(\begin{cases} & 3\leqslant 2x+y\leqslant 9 \\ & 6\leqslant x-y\leqslant 9 \\ \end{cases}\),则\(z=x+2y\)的最小值是_________.
\((3)\Delta ABC\)中,\(B=120{}^\circ ,AC=7,AB=5\),则\(\Delta ABC\)的面积为_________.
\((4)\)已知两个圆锥有公共底面,且两圆锥的顶点和底面的圆周都在同一个球面上\(.\)若圆锥底面面积是这个球面面积的\(\dfrac{3}{16}\),则这两个圆锥中,体积较小者的高与体积较大者的高的比值为________.