5.
\((1)\)若集合\(A=\{a-3,2a-1,a^{2}-4\}\),且\(-3∈A\),则实数\(a=\)________.
\((2)\)设向量\(a=(\sin 2θ,\cos θ)\),\(b=(\cos θ,1)\),则“\(a/\!/b\)”是“\(\tan θ= \dfrac{1}{2}\)成立”的_____条件\(.(\)选填“充分不必要”“必要不充分”“充要”“既不充分也不必要”\()\)
\((3)\)已知\(f(x)=\ln (x^{2}+1)\),\(g(x)=\left( \left. \dfrac{1}{2} \right. \right)^{x}-m\),若对\(∃x_{1}∈[0,3]\),\(∀ x_{2}∈[1,2]\),使得\(f(x_{1})\geqslant g(x_{2})\),则实数\(m\)的取值范围是________________.