Question

x³ + 8 + (x+2)(x-4) = 0

 

 

Answer 1

\(x^3+8+\left(x+2\right)\left(x-4\right)\)=0

\(\left(x+2\right)\left(x^2+2x+4\right)+\left(x+2\right)\left(x-4\right)\)=0

\(\left(x+2\right)\left(x^2+2x+4+x-4\right)\)=0

\(\left(x+2\right)\left(x^2+3x\right)\)=0

\(x\left(x+2\right)\left(x+3\right)\)=0

=>x=0, x=-2,x=-3

 

 

Answer 2

   x³+8+(x+2)(x-4)= 0
=> x³+8= 0     hoặc x+2= 0    hoặc x-4= 0
=> x³    = 0-8  hoặc x    = 0-2 hoặc x   = 0+4
=> x³    = -8    hoặc x    = -2   hoặc x   = 4
=> x      = -2