Question

30 ! ! решите уравнение: 1)х^3+6x^2-x-6=0 2)x^3-2x^2-9x+18=0

Answer 1

$1)x^3+6x^2-x-6=0 \\P(1)=1+6-1-6=0 \Rightarrow x_1=1 \\(x-1)(x^2+ax+b)=x^3+ax^2+bx-x^2-ax-b=\\=x^3+x^2(a-1)+x(b-a)-b \\x^3+6x^2-x-6=x^3+x^2(a-1)+x(b-a)-b \\ \left \{ {{a-1=6} \atop {b-a=-1}} \right. \Rightarrow \left \{ {{a=7} \atop {b=6}}\right. \\(x-1)(x^2+7x+6)=0 \\x^2+7x+6=0 \\D=49-24=25=5^2 \\x_2= \frac{-7+5}{2} =-1 \\x_3= \frac{-7-5}{2} =-6$
ответ: x1=1; x2=-1; x3=-6
$x^3-2x^2-9x+18=0 \\P(2)=8-8-18+18=0\Rightarrow x_1=2 \\(x-2)(x^2+ax+b)=x^3+ax^2+bx-2x^2-2ax-2b=\\=x^3+x^2(a-2)+x(b-2a)-2b \\x^3-2x^2-9x+18=x^3+x^2(a-2)+x(b-2a)-2b \\ \left \{ {{a-2=-2} \atop {b-2a=-9}} \right. \Rightarrow \left \{ {{a=0} \atop {b=-9}} \right. \\(x-2)(x^2-9)=0 \\x^2-9=0 \\x^2=9 \\x_2=3 \\x_3=-3$
ответ: x1=2; x2=3; x3=-3

Answer 2

ответ во вложении