x

_{1}' = -2x

_{1}+ x

_{2}+ x

_{3}

x

_{2}' = x

_{1}- x

_{2}+ 3x

_{3}

x

_{3}' = -x

_{2}- 3x

_{3}

Then I eliminated all variables except for x

_{2}, using Differentiation operator.

my AE from x

_{2}is this:

r

^{3}+ 6r

^{2}+ 12r + 12 = 0

And I'm stuck!

thank you in advance.