If $\alpha ,\beta ,\gamma$  are the roots of $x^3-2x^2+3x-4=0$ , then $\Sigma \alpha \beta \left(\alpha +\beta \right)=$

$=\Sigma {\alpha }^2\beta$

$={\alpha }^2\beta +{\alpha }^2\gamma +{\beta }^2\alpha +{\beta }^2\gamma +{\gamma }^2\alpha +{\gamma }^2\beta$

$=\alpha \beta \left(\alpha +\beta \right)+\beta \gamma \left(\beta +\gamma \right)+\alpha \gamma \left(\alpha +\gamma \right)$

$=\alpha \beta \left(2-\gamma \right)+\beta \gamma \left(2-\alpha \right)+\alpha \gamma \left(2-\beta \right)$

$=2\left(\alpha \beta +\beta \gamma +\gamma \alpha \right)-3\alpha \beta \gamma$

$\alpha \beta +\beta \gamma +\gamma \alpha =\frac{c}{a}=3,\alpha \beta \gamma =\frac{-d}{a}=4$

$=2\left(3\right)-3\left(4\right)$

$=6-12$

$=-6$