a.  -12 (x-5) +7(3-x) = -12x+60+21-7x=-19x+81=15

=> -19x=15-81=-66

=> x=66/19

b. 30(x+2) - 5 (x-5) - 24x = 30x+60-5x+25-24x =(30x-5x-24x)+(60+25)=x+85=100

=> x=100-85=15

c. ( 30x + 60 ) - ( 6x - 30 ) - 24x = 100

=30x+60-6x+30-24x

=90=100 (cô lý)

Vậy không có x thỏa mãn

=>-2x+12=10

hay x=11

\(\Leftrightarrow x-3\in\left\{1;-1;17\right\}\)

hay \(x\in\left\{4;2;20\right\}\)

\(\left(x-3\right)\inƯ\left(17\right)=\left\{1;17\right\}\)
\(=>\left[{}\begin{matrix}x=4\\x=20\end{matrix}\right.\)

\(\left(19-x:2\right)\inƯ\left(13\right)=\left\{1;13\right\}\)
\(=>\left[{}\begin{matrix}19-x:2=1\\19-x:2=13\end{matrix}\right.\)
\(=>\left[{}\begin{matrix}x=36\\x=12\end{matrix}\right.\)

13 ⋮ ( 19 – x :2) nha mọi người

\(\dfrac{x}{36}=\dfrac{76}{57}\)

 => \(\dfrac{x}{36}=\dfrac{4}{3}\)

=> \(\dfrac{x}{36}=\dfrac{48}{36}\)

=> x = 48

x-1 = 18 hoac y+5= 18

x=19 hoac y=13

(x-1).(y+5)=1.18=2.9

TH1{ x-1=1=> x=2

       {y+5=18 => y=13

TH2{x-1=18=> x=19

       {y+5=1 => y=-4

TH3{ x-1=2 => x=3

      {y+5=9 => y=4

TH4{x-1=9 => x=10

      {y+5=2 => y=-3

KL:.....

\(\dfrac{x-2}{5}=\dfrac{1-x}{6}\\ =>\left(x-2\right)\cdot6=\left(1-x\right)\cdot5\\ =>6x-12=5-5x\\ =>6x+5x=5+12\\ =>11x=17\\ x=\dfrac{17}{11}\)

`[x-2]/5=[1-x]/6`

`=>6(x-2)=5(1-x)`

`=>6x-12=5-5x`

`=>6x+5x=5+12`

`=>11x=17`

`=>x=17/11`

\(\Rightarrow\left[3\left(x+1\right)+8\right]⋮\left(x+1\right)\\ \Rightarrow x+1\inƯ\left(8\right)=\left\{-8;-4;-2;-1;1;2;4;8\right\}\\ \Rightarrow x\in\left\{-9;-5;-3;-2;0;1;3;7\right\}\)