Đáp án:
c) $\dfrac{x+2}{5}$ = $\dfrac{x-1}{2}$
⇔ $\dfrac{2(x+2)}{10}$ = $\dfrac{5(x-1)}{10}$
⇔ 2(x+2) = 5(x-1)
⇔ 2x+4 = 5x -5
⇔ 2x-5x =-5-4
⇔ -3x = -9
⇔ x = -9 : (-3)
⇔ x = 3
Vậy x = 3
Bài 4
a) $\dfrac{x-1}{x-5}$ = $\dfrac{6}{7}$
⇔ $\dfrac{7(x-1)}{7(x-5)}$ = $\dfrac{6(x-5)}{7(x-5)}$
⇔ 7(x-1) = 6(x-5)
⇔ 7x - 7 = 6x -30
⇔ 7x- 6x = -30 +7
⇔ x = -23
Vậy x = -23
b) $\dfrac{3}{x-4}$ = $\dfrac{27}{x+4}$
⇔ $\dfrac{3(x+4)}{(x-4)(x+4)}$ = $\dfrac{27(x-4)}{(x+4)(x-4)}$
⇔ 3(x+4) =27(x-4)
⇔ 3x + 12 = 27x - 108
⇔3x - 27x = -108 -12
⇔ -24x = -120
⇔ x = -120 : (-24)
⇔ x = 5
Vậy x = 5
