`3)`
\(a,\dfrac{1}{3}-\dfrac{2}{3}x=-2,5\\ =>\dfrac{1}{3}-\dfrac{2}{3}x=-\dfrac{25}{10}\\ =>\dfrac{1}{3}-\dfrac{2}{3}x=-\dfrac{5}{2}\\ =>\dfrac{2}{3}x=\dfrac{1}{3}-\left(-\dfrac{5}{2}\right)\\ =>\dfrac{2}{3}x=\dfrac{1}{3}+\dfrac{5}{2}\\ =>\dfrac{2}{3}x=\dfrac{2}{6}+\dfrac{15}{6}\\ =>\dfrac{2}{3}x=\dfrac{17}{6}\\ =>x=\dfrac{17}{6}:\dfrac{2}{3}\\ =>x=\dfrac{17.2}{6.3}\\ =>x=\dfrac{17.1}{2.3}\\ =>x=\dfrac{17}{6}\\ b,30\%x-0,5=-2,75\\ =>0,3x-0,5=-2,75\\ =>0,3x=-2,75+0,5\\ =>0,3x=-2,25\\ =>x=-2,25:0,3\\ =>x=-7,5\)
`4)`
\(a,\dfrac{2x+1}{12}=\dfrac{1}{-4}\\ =>2x+1:12=-\dfrac{1}{4}\\ =>2x+1=-\dfrac{1}{4}.12\\ =>2x+1=-\dfrac{12}{4}\\ =>2x+1=-3\\ =>2x=-3-1\\ =>2x=-4\\ =>x=-4:2\\ =>x=-2\\ b,\left(2\dfrac{1}{5}+\dfrac{3}{5}x\right):\dfrac{1}{3}=\dfrac{3}{4}\\ =>\dfrac{11}{5}+\dfrac{3}{5}x=\dfrac{3}{4}.\dfrac{1}{3}\\ =>\dfrac{11}{5}+\dfrac{3}{5}x=\dfrac{1}{4}\\ =>\dfrac{3}{5}x=\dfrac{1}{4}-\dfrac{11}{5}\\ =>\dfrac{3}{5}x=\dfrac{5}{20}-\dfrac{44}{20}\\ =>\dfrac{3}{5}x=-\dfrac{29}{20}\\ =>x=-\dfrac{29}{20}:\dfrac{3}{5}\\ =>x=-\dfrac{29}{20}.\dfrac{5}{3}\\ =>x=-\dfrac{29.5}{20.3}\\ =>x=-\dfrac{29.1}{4.3}\\ =>x=-\dfrac{29}{12}\)
Bài `3`
`a,1/3-2/3 .x=-2,5`
`=> 2/3 .x=1/3- (-2,5)`
`=> 2/3 .x=1/3+2,5`
`=> x= 1/3+2,5 : 2/3`
`=> 2/3x= 1/3+2,5`
`=> 2/3x=17/6`
`=>x= 17/6 xx 3/2`
`=>x=17/4`
`b,30%.x-0,5=-2,75`
`=> 30%.x=-2,75+0,5`
`=> 30%.x=-2,25`
`=>x= -2,25 : 3/10`
`=>x= -2,25 xx 10/3`
`=>x= -7,5`
Bài `4`
`a, (2x+1)/12=1/(-4)`
`=> (2x+1).(-4)=12`
`=>2x+1=12:(-4)`
`=>2x+1=-3`
`=>2x=-3-1`
`=>2x=-4`
`=>x=-4:2`
`=>x=-2`
`b, ( 2 1/5+3/5x):1/3=3/4`
`=> ( 11/5 +3/5x):1/3=3/4`
`=> 11/5 +3/5x=3/4 xx 1/3`
`=> 11/5 +3/5x=1/4`
`=> 3/5x= 1/4-11/5`
`=> 3/5x=-1,95`
`=>x=-1,95 : 3/5`
`=>x=-3,25`
cậu tách ra 2 bài 1 lần thôi đăng nhiều v ko ai làm đâu á⚡
Bài 5
1/4 + 1/3 : (2x - 1) = -5
1/3 : (2x - 1) = -5 - 1/4
1/3 : (2x - 1) = -21/4
2x - 1 = 1/3 : (-21/4)
2x - 1 = -4/63
2x = -4/63 + 1
2x = 59/63
x = 59/63 : 2
x = 59/126
-------------------
Bài 6
a) x - 1/7 = 6/35
x = 6/35 + 1/7
x = 11/35
b) 5/11 : x + 4/9 = 1/6
5/11 : x = 1/6 - 4/9
5/11 : x = -5/18
x = 5/11 : (-5/18)
x = -18/11
Bài 7
a) 1/7 - 2/7 . x = 20%
2/7 . x = 1/7 - 20%
2/7 . x = -2/35
x = -2/35 : 2/7
x = -1/5
b) 14/x = -7/3
x = 14 . 3 : (-7)
x = -6
-------------------
Bài 8
a) (3 1/5 + 1 3/5 x) : 1/3 = 3/4
16/5 + 8/5 x = 3/4 . 1/3
16/5 + 8/5 x = 1/4
8/5 x = 1/4 - 16/5
8/5 x = -59/20
x = -59/20 : 8/5
x = -59/32
b) 1/3 : (3x + 1) - 1/4 = -5
1/3 : (3x + 1) = -5 + 1/4
1/3 : (3x + 1) = -19/4
3x + 1 = 1/3 : (-19/4 )
3x + 1 = -4/57
3x = -4/57 - 1
3x = -61/57
x = -61/57 : 3
x = -61/171