ok , nhìn qua thì đề bài đã sai rồi , để tui sửa nha : 

Tìm \(m\in Z\)sao cho \(m+4\)chia hết cho \(m-3\)

Ta có \(m-3⋮m+4\)

\(\Rightarrow m+4-4-3⋮m+4\)

\(\Rightarrow m+4-7⋮m+4\)

\(\Rightarrow-7\Rightarrow m+4\Rightarrow m+4\inƯ\left(7\right)\)

Mà \(Ư\left(7\right)=\left\{1;7;-1;-7\right\}\)

Suy ra \(m\in\left\{-3;3;-4;-11\right\}\)

\(\frac{2x+5}{7}=\frac{3-x}{2}\)Theo quy tắc nhân chéo => 7(3-x) = 2(2x+5)

=> 21 - 7x = 4x +10

=> -11x = -11

=> x = 1

<=> (2x+5)2= (3-x)7

<=> 4x+10=21-7x

<=>4x+10-21+7x=0

<=> 11x=11

=> x=1

 ta co\(\frac{6x}{11}=\frac{9y}{2}=\frac{18z}{5}\)\(=\frac{x}{\frac{11}{6}}=\frac{y}{\frac{2}{9}}=\frac{z}{\frac{5}{18}}\)=\(\frac{-x+y+z}{\frac{11}{6}+\frac{2}{9}+\frac{5}{18}}=\frac{120}{\frac{-4}{3}}=-90\)(ap dung tinh chat day ti so bang nhau)

\(\frac{x}{\frac{11}{6}}=-90->x=-165\)lam tuong tu ta duoc y=-20,z=-25 sau do ban do ban doi dau thi duoc x=165,y=20,z=25

có

đó là: 3.5/5.25=14/21 ; 3.5/14=5.25/21 ; 21/5.25=14/3.5 ; 5.25/3.5=21/14

ta co 6/11.x=20

x=20.11/6

x=110/3

ta co 9/2y=20 

y=20.2/9=40/9

ta co 18/5 z=20

z= 20.5/18

z=50/9

\(x=20:\frac{6}{11}=\frac{110}{3}\)

\(y=20:\frac{9}{2}=\frac{40}{9}\)

\(z=20:\frac{18}{5}=\frac{50}{9}\)