2.
下列四个命题中,真命题的序号有 ________________\((\)写出所有真命题的序号\()\).
\(①\)函数\(y=\left| x+1 \right|+\left| x-1 \right|\)的最小值是\(2\) ;
\(②\)圆\(x^{2}+y^{2}+4x-2y+1=0\)与直线\(y=\dfrac{1}{2}x\)相交,所得弦长为\(2\) ;
\(③\)将函数\(y=\left| x+1\left. {} \right| \right.\)的图象向左平移一个单位,得到的图象对应的函数表达式为\(y=\left| x\left. {} \right| \right.\) ;
\(④\)若\(\sin (\alpha +\beta )=\dfrac{1}{2} \),\(\sin (\alpha -\beta )=\dfrac{1}{3}\),则\(\tan \alpha =5\tan \beta \).