\(a,\text{A nguyên }\Leftrightarrow2n+7⋮n+2\)

\(\text{Ta có : }n+2⋮n+2\)

\(\Rightarrow\left(2n+7\right)-\left(n+2\right)⋮n+2\)

\(\Rightarrow2n+7-n-2⋮n+2\)

\(\Rightarrow5⋮n+2\)

\(\Rightarrow n+2\in\text{Ư}\left(5\right)=\left\{1;-1;5;-5\right\}\)

\(\Rightarrow n\in\left\{-1;-3;3;-7\right\}\)

\(b,\text{Ta có : }A=\frac{2n+7}{n+2}\)

\(=\frac{n+2+n+2+3}{n+2}\)

\(=2+\frac{3}{n+2}\)

A tối giản <=> ƯCLN ( 2n + 7; n + 2 )  = 1

\(\Leftrightarrow\text{Ư}CLN\left(3;n+2\right)=1\)

\(\Leftrightarrow n+2\) \(⋮̸\)\(3\)

\(\Leftrightarrow n+2\ne3d\left(d\in N\right)\)

\(\Leftrightarrow n\ne3d-2\left(d\in N\right)\)

Vậy .... 

3x = 51/42 = 17/14→ 3x = 3x/1 = 14.3x/14 = 42x/14 = 17/14→ 42x = 17→ x = 17/42

3x = 51/42 = 17/14→ 3x = 3x/1 = 14.3x/14 = 42x/14 = 17/14→ 42x = 17→ x = 17/42

ok nhưng xẽ có lời giải sau đây

3x=51/42
(=)x=51/42:3
(=)x=17/42
Vậy x=17/42

333x333=110889

222x22=4884

ok chưa bạn

333x333=110889

222x22=4884

ccccccccccccccccccccccccccc

có 10 cây cau trồng thành 5 hàng mỗi hàng có 4 cây ????

Bài 5: 

a) Đặt \(\left(3n+2,5n+3\right)=d\).

\(\Rightarrow\hept{\begin{cases}3n+2⋮d\\5n+3⋮d\end{cases}}\Rightarrow5\left(3n+2\right)-3\left(5n+3\right)=1⋮d\Rightarrow d=1\).

suy ra đpcm. 

b) Đề bài sai. 

Ví dụ: với \(n=3\): \(\frac{3n+2}{7n+1}=\frac{11}{22}\)không là phân số tối giản. 

\(RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG\)

Help mik với làm ơn