4.
\((1)\)已知向量\(a\),\(b\)的夹角为\(60^{\circ}\),\(|a|=2\), \(|b |=1\),则\(|a +2b |= \)______ .
\((2).\)设\(x\),\(y\)满足约束条件\(\begin{cases} & x+2y\leqslant 1 \\ & 2x+y\geqslant -1 \\ & x-y\leqslant 0 \end{cases}\),则\(z=3x-2y\)的最小值为 ______ .
\((3)\)已知\(α∈\left(0, \dfrac{π}{2}\right),\tan α=2 \),则\(\cos \left(α- \dfrac{π}{4}\right) =\)______ .
\((4)\)已知三棱锥\(S-ABC\)的所有顶点都在球\(O\)的球面上,\(SC\)是球\(O\)的直径,若平面\(SCA⊥\)平面\(SCB\),\(SA=AC\),\(SB=BC\),三棱锥\(S-ABC\)的体积为\(9\),则球\(O\)的表面积为______ .