Question

9x2-1+(3x-1)(x+2=0

Answer 1

Lời giải:

$9x^2-1+(3x-1)(x+2)=0$

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

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

$\Leftrightarrow (3x-1)(4x+3)=0$

$\Leftrightarrow 3x-1=0$ hoặc $4x+3=0$

$\Leftrightarrow x=\frac{1}{3}$ hoặc $x=\frac{-3}{4}$

Answer 2

9x² - 1 + (3x - 1)(x + 2) = 0

\(\Leftrightarrow\) 9x² - 1 + 3x² + 6x - x - 2 = 0

\(\Leftrightarrow\) 12x² + 5x - 3 = 0

\(\Leftrightarrow\) 12x² - 4x + 9 x - 3 = 0

\(\Leftrightarrow\) (12x² - 4x) + (9x - 3) = 0

\(\Leftrightarrow\) 4x(3x - 1) + 3(3x - 1) = 0

\(\Leftrightarrow\) (3x - 1)(4x + 3) = 0

\(\Leftrightarrow\) \(\left[{}\begin{matrix}3x-1=0\\4x+3=0\end{matrix}\right.\) \(\Leftrightarrow\) \(\left[{}\begin{matrix}x=\dfrac{1}{3}\\x=\dfrac{-3}{4}\end{matrix}\right.\) 

S = \(\left\{\dfrac{1}{3},\dfrac{-3}{4}\right\}\)