x的三次方减去13乘x的平方加8x加4等于0
x^3-13x^2+8x+4=0
x^3-x^2-12x^2+8x+4=0
x^2(x-1)-4(3x^2-2x-1)=0
x^2(x-1)-4(3x+1)(x-1)=0
(x^2-4(3x+1))(x-1)=0
(x^2-12x-4)(x-1)=0
x-1=0 x^2-12x-4=0
x=1
或 x^2-12x-4=0
x^2-12x+36-36-4=0
（x+6）^2=40
x=-6+2√10或x=-6-2√10