[tex] x^{2} +ax-2a=0 , \ a \in R[/tex]
[tex]ax^2+bx+x=0 \ \ a,b,c \in R \ , a \neq 0[/tex]
[tex]\rightarrow \left \{ {{a=1} \atop {b=a}} \atop {c=-2a}} \right. [/tex]
[tex]S=x_1+x_2= \frac{-b}{a} = \frac{-a}{1} = -a
[/tex]
[tex]P=x_1*x_2= \frac{c}{a} = \frac{-2a}{1}= -2a [/tex]
[tex]2(x_1+x_2)-x_1*x_2= 2S-P= 2*(-a)-(-2a)=-2a+2a=0 [/tex]
