Question

\(x^3+8+\left(x+2\right)\left(2x+5\right)=0\\ \)

Answer 1

\(x^3+8+\left(x+2\right)\left(2x+5\right)=0\)

\(\Leftrightarrow\left(x+2\right)\left(x^2-2x+4\right)+\left(x+2\right)\left(2x+5\right)=0\)

\(\Leftrightarrow\left(x+2\right)\left(x^2+9>0\right)=0\Leftrightarrow x=-2\)

Answer 2

=(x+2)(x^2 -2x+4)+(x+2)(2x+5)=0

=(x+2)(x^2 +9)=0

=>x+2=0            hoặc x^2=-9(loại)

=>x=-2

Answer 3

Ta có: \(x^3+8+\left(x+2\right)\left(2x+5\right)=0\)

\(\Leftrightarrow\left(x+2\right)\left(x^2-2x+4+2x+5\right)=0\)

\(\Leftrightarrow x+2=0\)

hay x=-2