5.
\((1)\)单项式\(-2a{{b}^{2}}\)的系数是 .
\((2)\)比较:\({2}{{{8}}^{0}}{15 }\!\!{{'}}\!\!{ }\) \({{28.15}^{0}}(\)填“\( > \)”、“\( < \)”或“\(=\)”\()\).
\((3)\)点\(A\),\(B\),\(C\)在同一条直线上,\(AB\)\(=3\)\(cm\),\(BC\)\(=1\)\(cm\),则\(AC\)\(=\) .
\((4)\)定义运算\(a\)\(\otimes \) \(b\)\(=\)\(a\)\((1-\)\(b\)\()\),下面给出了关于这种运算的四个结论:
\(①2\otimes (-2)=6\) \(②\)\(a\)\(\otimes \) \(b\)\(=\)\(b\)\(\otimes \) \(a\)
\(③\)若\(2\otimes \) \(a\)\(=0\),则\(a\)\(=1\) \(④\)\(a\)\(\otimes 1=0\)
其中正确结论的序号是 \((\)填上你认为所有正确结论的序号\()\)