Question

Tìm x: 2x^3+ 7x^2+7x+2 =0

Answer 1

Ta có : 2x³+ 7x²+7x+2 =0

<=> \(2\left(x^3+1\right)+7x\left(x+1\right)=0\)

<=> \(2\left(x+1\right)\left(x^2-x+1\right)+7x\left(x+1\right)=0\)

<=> \(\left(x+1\right)\left(2x^2-2x+2+7x\right)=0\)

<=> \(\left(x+1\right)\left(2x^2+5x+2\right)=0\)

<=> \(\left(x+1\right)\left(2x+1\right)\left(x+2\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x=-1\\x=-0,5\\x=-2\end{matrix}\right.\)

Answer 2

2x³+7x²+7x+2=0=>2(x³+1)+7x(x+1)=0

=>2(x+1)(x²-x+1)+7x(x+1)=0

=>(x+1)(2x²-2x+2+7x)=0

=> x = -1 hoặc 2x²+5x+2=0

=>2x²+4x+x+2=0

=>2x(x+2)+(x+2)=0

=>(x+2)(2x+1)=0

=>x=-1 hoặc x=-2 hoặc x=\(\dfrac{-1}{2}\)