x^3-2x^2-3x+6=0,
x^3-2x^2-3x+6=0,
x^2(x-2)-3(x-2)=0,
(x-2)(x^2-3)=0,
(x-2)(x-√3)(x+√3)=0,
x-2=0, x-√3=0, x+√3=0,
x1=2, x2=√3, x3=-√3;
;
x^4-5x^2+4=0,
x^4-x^2-4x^2+4=0,
x^2(x^2-1)-4(x^2-1)=0,
(x^2-1)(x^2-4)=0,
(x-1)(x+1)(x-2)(x+2)=0,
x-1=0, x+1=0, x-2, x+2=0,
x1=1, x2=-1, x3=2, x4=-2,
x^3+2x^2-5x-6=0,
x^3+x^2-6x+x^2+x-6=0,
x(x^2+x-6)+(x^2+x-6)=0,
(x^2+x-6)(x+1)=0,
(x^2-2x+3x-6)(x+1)=0,
(x(x-2)+3(x-2)(x+1)=0,
(x-2)(x+3)(x+1)=0,
x-2=0, x+3=0, x+1=0,
x=2, x=-3, x=-1