\((1)\)计算\(\cos \dfrac{5\pi }{3}\)的值为_______.
\((2)\)在\({{(x+\dfrac{2}{{{x}^{2}}})}^{6}}\)的展开式中,常数项为_______\(.(\)用数字作答\()\)
\((3)\)某人欲把\(a\),\(b\)两盆红色花和\(c\),\(d\)两盆紫色花放在一排四个花台上,若\(b\),\(c\)两盆花必须相邻,则不同的放法共有_______种.
\((4)\)若函数\(f(x)=\lg ({{10}^{x}}+1)+ax\)是偶函数,则实数\(a=\)_______.