Câu hỏi của Lil Học Giỏi

Question

Tìm x , biết :

1, x3 - 2x2 - 2x = 0

2, 2x3 - 5x2 + 8x - 3 = 0

3, 3x3 - 14x2 + 4x + 3 = 0

4, x3 + 6x2 - 5x = 0

Nguyễn Việt Lâm · Accepted Answer

a/ $x\left(x^2-2x-2\right)=0$

$\Rightarrow\left[{}\begin{matrix}x=0\x=1\pm\sqrt{3}\\end{matrix}\right.$

b/ $\Leftrightarrow2x^3-4x^2+6x-x^2+2x-3=0$

$\Leftrightarrow2x\left(x^2-2x+3\right)-\left(x^2-2x+3\right)=0$

$\Leftrightarrow\left(2x-1\right)\left(x^2-2x+3\right)=0$

c/ $\Leftrightarrow3x^3-15x^2+9x+x^2-5x+3=0$

$\Leftrightarrow3x\left(x^2-5x+3\right)+\left(x^2-5x+3\right)=0$

$\Leftrightarrow\left(3x+1\right)\left(x^2-5x+3\right)=0\Rightarrow\left[{}\begin{matrix}x=-\frac{1}{3}\x=\frac{5\pm\sqrt{13}}{2}\end{matrix}\right.$

d/ $x\left(x^2+6x-5\right)=0\Rightarrow\left[{}\begin{matrix}x=0\x=-3\pm\sqrt{14}\end{matrix}\right.$Câu trả lời: a/ $x\left(x^2-2x-2\right)=0$