Question

x^4 + 18x^3 +81 x^2 =0​

Answer 1

$x^4+18x^3+81x^2=0;\\x^2(x^2+18x+81)=0;\\x^2(x+9)^2=0.$

$x=0$ или $x+9=0$,

$x=0$ или $x=-9$