2x(x+20)^2-x^2(x+20)=0
2x(x^2+40x+400)-x^3-20x^2=0
2x^3+80x^2+800x-x^3-20x^2=0
x^3+60x^2+800x=0
x(x^2+60x+800)=0
x1=0
x^2+60x+800=0
D=60^2-4*1*800=3600-3200=400
x1=-60+√400=-60+20=-40\2=-20
2 2
x2=-60-√400=-60-20=-80\2=-40
2 2
Ответ: x1=-40; x2=-20; x3=0