[tex]W(x)= 2x^3-5x^2-8x+20 =x^2(2x-5)-4(2x-5)=(2x-5)(x^2-4)=\\\\=(2x-5)(x-2)(x+2)\\\\\\pierwiastki wielomianu:\\\\(2x-5)(x-2)(x+2)=0\\\\2x-5=0\ \ lub\ \ x-2=0\ \ lub\ \ x+2=0\\\\2x=5 \ \ lub\ \ x=2 \ \ lub\ \ x=-2\\\\x=\frac{5}{2}\\\\x\in\left\{ -2,2,\frac{5}{2}\right\}[/tex]
