6.
\((1)\)设\(x\),\(y\)满足约束条件\(\begin{cases} & 2x-y-2\leqslant 0 \\ & x-2y+2\geqslant 0 \\ & x+y-2\geqslant 0 \end{cases}\),若\(z=mx+y\)取得最大值时的最优解有无穷多个,则实数\(m\)的值是__________.
\((2)\)设平面向量\(a=\left( x,4 \right),b=\left( y,-2 \right),c=\left( 2,1 \right)\),\((\)其中\(x > 0,y > 0)\)若\(\left( a-c \right)\bot \left( b-c \right)\),则\(\left| a+b \right|\)的最小值为______.
\((3)\)如下图,在\(\Delta ABC\)中,\(AB=AC,BC=2, \overrightarrow{AD}= \overrightarrow{DC}, \overrightarrow{AE}= \dfrac{1}{2} \overrightarrow{EB} .\)若,则\( \overrightarrow{CE}· \overrightarrow{AB} \) __________.
\((4)\)已知函数\(f\left( x \right)=2x-{\cos }x\),数列\(\left\{ {{a}_{n}} \right\}\)是公差为\(\dfrac{\pi }{8}\)的等差数列,若\(f\left( {{a}_{1}} \right)+f\left( {{a}_{2}} \right)+f\left( {{a}_{3}} \right)+f\left( {{a}_{4}} \right)+f\left( {{a}_{5}} \right)=5\pi \),则\({{\left[ f\left( {{a}_{3}} \right) \right]}^{2}}-{{a}_{1}}{{a}_{5}}=\)__________.