S = -1 => x = -1
inlocuim x
[tex]2 \times {( - 1)}^{2} + a \times ( - 1) + 3 = 0[/tex]
[tex]2 \times 1 + ( - a) + 3 = 0[/tex]
[tex]2 - a + 3 = 0[/tex]
[tex]5 - a = 0[/tex]
[tex] - a = 0 - 5[/tex]
[tex] - a = - 5[/tex]
[tex]a = - 5 \times ( - 1)[/tex]
[tex]a = 5[/tex]