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[tex]\displaystyle x^2+px+q=0\\\\\left \{ {{x_1+x_2=-p} \atop {x_1*x_2=q}} \right.[/tex]

тогда

[tex]\displaystyle x^2+px-30=0\\\\\left \{ {{x_1+x_2=-p} \atop {x_1*x_2=-30}} \right. \\\\x_1=-10\\\\-10*x_2=-30\\\\x_2=3\\\\-10+3=-7\\\\-7=-p\\\\p=7\\\\x^2+7x-30=0[/tex]

Ответ:

x²+px-30=0

x1×x2=-30

-10×x2=30

x2=3

x1+x2=p

-10+3=-7

x2+7x-30=0