Question

tìm x biết

5x (x-3) - 2x + 6 =0

x^3 + 5x^2 - 4x - 20=0

Answer 1

`5x (x-3) - 2x + 6 =0`

`<=>5x (x-3) -(2x-6)=0`

`<=> 5x (x-3) -2(x-3)=0`

`<=>(x-3)(5x-2)=0`

\(\Leftrightarrow\left[{}\begin{matrix}x-3=0\\5x-2=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=3\\x=\dfrac{2}{5}\end{matrix}\right.\)

`-----------`

`x^3 + 5x^2 - 4x - 20=0`

`<=>x^2(x+5)-(4x + 20)=0`

`<=>x^2(x+5)-4(x+5)=0`

`<=>(x+5)(x^2-4)=0`

\(\Leftrightarrow\left[{}\begin{matrix}x+5=0\\x^2-4=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-5\\x=\pm2\end{matrix}\right.\)