Question

x^4+2x^3-9x^2+6x+9＝0

Answer 1

(x^4-3x^3+3x^2)+(5x^3-15x^2+15x)+(3x^2-9x+9)=0

x^2(x^2-3x+3)+5x(x^2-3x+3)+3(x^2-3x+3)=0

(x^2-3x+3)(x^2+5x+3)=0

x^2-3x+3=0无实根；

x^2+5x+3=0得：x= (-5±√13)/2