a) $(3x -2 )$ . $( 4x+5 )$ =0
⇔ $3x-2 $ =0 hay $4x+5$ = 0
⇔ $3x $ = $2$ $4x$ = -5
⇔ $x$ = $\frac{2}{3}$ $x$ = $\frac{-5}{4}$
Vậy S ={$\frac{2}{3}$ ; $\frac{-5}{4}$ }
b)$(2,3x - 6,9 )$ . $(0,1x + 2) $ = 0
⇔$(2,3x - 6,9 )$ = 0 hay (0,1x + 2) = 0
⇔ $2,3x $ = $6,9$ $0,1x$ = $-2$
⇔ $x$ = $3$ $x$ = $-20$
Vậy S={3;-20}
c)$(4x+2)$ .$(x²+1)$ =0
⇔ $4x+2$ =0 hay $x² + 1$ = 0
⇔ $4x$ = $-2$ x² = -1 ( vô lí ) ( loại )
⇔ x = $\frac{-1}{2}$
Vậy S={$\frac{-1}{2}$ }
CHo tui ctlhn nha ! <3 O_o
