x^3-5x+4=0
-5x=-x-4x
x^3-x-4x+4=0
x(x^2-1)-4(x-1)=0
x(x-1)(x+1)-4(x-1)=0
(x-1)[x(x+1)-4]=0
(x-1)(x^2+x-4)=0
x-1=0 lub x^2+x-4=0
x_1=1
lub
x^2+x-4=0
\Delta=1+16=17
x_2=\frac{-1-\sqrt{17}}{2}=-0,5-0,5\sqrt{17}
x_3=\frac{-1+\sqrt{17}}{2}=-0,5+0,5\sqrt{17}