Question

Giải PT : x³-2x+4=0

Answer 1

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)(x²+2x+2) = 0

=> x+2=0 hoặc x²+2x+2=0

=> x=-2 hoặc (x+1)²=-1(vô lí)

Vậy: x=-2

Answer 2

Có pt: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)(x²+2x+2)=0

*TH1:x+2=0 *TH2:x²+2x+2=0

x =-2 x(x+2) =-2

<=>x=-2 x=-4