(x+2)^4-x^4=80
[(x+2)^2]^2-x^4=80
(x^2+4x+4)^2-x^4=80
[(x^2+4x)+4]^2-x^4=80
x^4+8x^3+16x^2+8(x^2+4x)+16-80=0
8x^3+16x^2+8x^2+32x-64=0
8x^3+24x^2+32x-64=0|:8
x^3+3x^2+4x-8=0 …3x^2=-x^2+4x^2 i 4x=-4x+8x
metoda grupowania wyrazów
x^3-x^2+4x^2-4x+8x-8=0
x^2(x-1)+4x(x-1)+8(x-1)=0
(x-1)(x^2+4x+8)=0
x-1=0
x=1
lub
x^2+4x+8=0
a=1, b=4, c=8
\Delta=b^2-4ac=16-4*4*8=16-128=-112
\Delta<0 brak pierwiastków
x=1