<=> 2x -10 - (3x+21) = 14

<=> 2x - 10 - 3x - 21 - 14 = 0

<=> -x -45 = 0

<=> x = -45

     2.(x-5) - 3.(x+7) = 14

=> 2x - 10 - 3x + 21 = 14

=> (2x - 3x) + (-10 + 21) = 14

=> (-x) + 11 = 14

=> -x           = 14 - 11

=> -x           = 3

=> x            = -3

    Vậy x = -3

Ta có: \(\frac{1}{a\left(a+1\right)}-\frac{1}{\left(a+1\right)\left(a+2\right)}=\frac{a+2}{a\left(a+1\right)\left(a+2\right)}-\frac{a}{a\left(a+1\right)\left(a+2\right)}\)

                                                                          \(=\frac{a+2-a}{a\left(a+1\right)\left(a+2\right)}=\frac{2}{a\left(a+1\right)\left(a+2\right)}\left(đpcm\right)\)

Ta có: \(\frac{3}{x}=\frac{y}{35}=\frac{\left(-36\right)}{84}\)

\(\left(-36\right).35=y.84\Leftrightarrow\left(-1260\right)=y.84\)

\(\Rightarrow y=\left(-15\right)\)

\(\Leftrightarrow3.35=x.\left(-15\right)\)

\(\Leftrightarrow105=x.\left(-15\right)\Rightarrow x=\left(-7\right)\)

\(\Rightarrow\orbr{\begin{cases}x=\left(-7\right)\\y=\left(-15\right)\end{cases}}\)

3. Gọi d là ƯCLN(2n + 3, 4n + 8), d ∈ N*

\(\Rightarrow\hept{\begin{cases}2n+3⋮d\\4n+8⋮d\end{cases}\Rightarrow\hept{\begin{cases}2\left(2n+3\right)⋮d\\4n+8⋮d\end{cases}\Rightarrow}\hept{\begin{cases}4n+6⋮d\\4n+8⋮d\end{cases}}}\)

\(\Rightarrow\left(4n+8\right)-\left(4n+6\right)⋮d\)

\(\Rightarrow2⋮d\)

\(\Rightarrow d\in\left\{1;2\right\}\)

Mà 2n + 3 không chia hết cho 2

\(\Rightarrow d=1\)

\(\RightarrowƯCLN\left(2n+3,4n+8\right)=1\)

\(\Rightarrow\frac{2n+3}{4n+8}\) là phân số tối giản.

5^2x - 3 - 2 . 5^2 = 5^2 . 3

5^2x - 3 - 2 . 5^2 = 75

5^2 - 3                 = 75 + 50

5^2 - 3                 = 125

Ta có: 25 = 5 . 5 . 5

=> 2x - 3 = 3

     2x      = 6

       x      = 6 : 2

       x      = 3

trả lừoi

x=3

nha

hok tốt

mk nè

kb nha

nhớ k mk đó

chào bn

có mk nek,