giúp mik với mik hứa sẽ cho các bạn 5 vote mik cần gấp ạ .
Chú ý : / là dấu của phân số .
Bài 1 :
a)x – 1 / 5 = x + 3 / 3
b) 3/ x- 1 = 21/16 .
c) 6,12 / 3 = 0 ,12 / x .
d) x / 6 = 7 /4 .
e) 3/ x = 21 / 16 .
f) 2x + 4 / 7 = 4x – 2 / 15 .
g) 2x + 3 / 24 = 3x -1 / 32 .
Đáp án:
Bài 1 :
$a) \dfrac{x-1}{5} = \dfrac{x+3}{3}$
$⇔\dfrac{3(x-1)}{15} =\dfrac{5(x+3)}{15}$
$⇔ 3(x-1) = 5(x+3)$
$⇔ 3x-3 = 5x+15$
$⇔3x-5x = 15 +3$
$⇔ -2x = 18$
$⇔x = 18 : (-2)$
$⇔x = -9$
Vậy $x=-9$
$b) \dfrac{3}{x-1} =\dfrac{21}{16}$
$\text{ĐKXĐ: x $\neq$ 1 }$
$⇔\dfrac{48}{16(x-1)} =\dfrac{21(x-1)}{16(x-1)}$
$⇔ 48 = 21(x-1)$
$⇔ 48 = 21x-21$
$⇔-21x = -21 -48$
$⇔ -21x = -69$
$⇔x = -69 : (-21)$
$⇔x =\dfrac{23}{7}$ (thỏa mãn)
Vậy $x=\dfrac{23}{7}$
$c) \dfrac{6,12}{3} =\dfrac{0,12}{x}$
$\text{ĐKXĐ : x $\neq$ 0}Ư$
$⇔ \dfrac{6,12x}{3x} =\dfrac{0,36}{3x}$
$⇔ 6,12x = 0,36$
$⇔x = 0,36 : 6,12$
$⇔x= \dfrac{1}{17}$
Vậy $x=\dfrac{1}{17}$
$d) \dfrac{x}{6} =\dfrac{7}{4}$
$⇔x = \dfrac{6.4}{7} = \dfrac{24}{7}$
Vậy $x=\dfrac{24}{7}$
$e) \dfrac{3}{x} =\dfrac{21}{16}$
$⇔x =\dfrac{3.16}{21}$
$⇔x=\dfrac{16}{7}$
Vậy $x=\dfrac{16}{7}$
$f) \dfrac{2x+4}{7} =\dfrac{4x-2}{15}$
$⇔\dfrac{15(2x+4)}{105} =\dfrac{7(4x-2)}{105}$
$⇔15(2x+4) = 7(4x-2($
$⇔ 30x + 60 = 28x – 14$
$⇔30x-28x = -14 -60$
$⇔2x =-74$
$⇔x = -74 : 2$
$⇔x=-37$
Vậy $x=-37$
$g) \dfrac{2x+3}{24} =\dfrac{3x-1}{32}$
$⇔\dfrac{32(2x+3)}{768} =\dfrac{24(3x-1)}{768}$
$⇔32(2x+3) = 24(3x-1)$
$⇔ 64x + 96 = 72x – 24$
$⇔ 64x – 72x = -24 -96$
$⇔-8x = -120$
$⇔x = -120 : (-8)$
$⇔x=15$
Vậy $x=15$