a) 2(3x-1)=x+3
⇔ 6x -2 =x +3
⇔ 6x-x=3+2
⇔ 5x=5
⇔ x=1
b) x² + 4x +3 =0
⇔ x²+x+3x+3
⇔ x(x+1) +3(x+1) =0
⇔ (x+1)(x+3) =0
⇔ $\left \{ {{x+1=0} \atop {x+3=0}} \right.$
⇔$\left \{ {{x=-1} \atop {x=-3}} \right.$
c) |x-13|=5
⇒ x-13=5 hoặc x-13 =-5
+) x-13 =5 +) x-13 =-5
⇔x=18 ⇔ x=8
d ) $\frac{x}{x+3}$ + $\frac{4}{x-3}$ = $\frac{x²}{x²-9}$ (1)
*ĐKXĐ : x khác 3 và -3
(1)⇔$\frac{x(x-3)}{(x+3)(x-3)}$ + $\frac{4(x+3)}{(x+3)(x-3)}$ - $\frac{x²}{(x-3)(x+3)}$ = 0
⇔ $\frac{x(x-3) + 4(x+3) - x²}{(x-3)(x+3)}$ = 0
⇔ $\frac{x²-3x+4x+12-x²}{(x-3)(x+3)}$ = 0
⇔ $\frac{x+12}{(x-3)(x+3)}$ = 0
⇒ x+12 = 0
⇔ x=-12
