$\{\begin{array}{l}W\left(2\right)=-6\\ W\left(-1\right)=6\end{array}$  

$\{\begin{array}{l}{2}^3-2\cdot 2^2+a\cdot 2+b=-6\\ {\left(-1\right)}^3-2\cdot {\left(-1\right)}^2+a\cdot \left(-1\right)+b=6\end{array}$  

$\{\begin{array}{l}8-2\cdot 4+2a+b=-6\\ -1-2\cdot 1-a+b=6\end{array}$  

$\{\begin{array}{l}8-8+2a+b=-6\\ -1-2-a+b=6\end{array}$  

$\{\begin{array}{l}2a+b=-6\\ -a+b=9\end{array}$  

$\{\begin{array}{l}2a+b=-6\\ b=a+9\end{array}$  

Podstawiamy b=a+9 do pierwszego równania w układzie.

$\{\begin{array}{l}2a+a+9=-6\\ b=a+9\end{array}$  

$\{\begin{array}{l}3a=-15\mid :3\\ b=a+9\end{array}$  

$\{\begin{array}{l}a=-5\\ b=a+9\end{array}$  

Podstawiamy a=-5 do drugiego równania w układzie.

$\{\begin{array}{l}a=-5\\ b=-5+9\end{array}$  

$\{\begin{array}{l}a=-5\\ b=4\end{array}$  

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$\text{Odp.}a=-5,b=4.$