x³=2x+4
x³-2x-4=0
x³-4x+2x-4=0
x·(x²-4)+2(x-2)=0
x·(x-2)·(x+2)+2(x-2)=0
(x-2)·(x·(x+2)+2)=0
(x-2)·(x²+2x+2)=0
x-2=0
x²+2x+2=0
x=2
x⊄R
x³=2x+4
x³-2x-4=0
x³-4x+2x-4=0
x·(x²-4)+2(x-2)=0
x·(x-2)·(x+2)+2(x-2)=0
(x-2)·(x·(x+2)+2)=0
(x-2)·(x²+2x+2)=0
x-2=0
x²+2x+2=0
x=2
x⊄R
x=2