viết rõ ra bạn 

9

`1/3 + 1/2 : x  =-4`

`1/2 :x = (-4) - 1/3`

`1/2:x=(-12)/3 - 1/3`

`1/2:x=(-13)/3`

`x=1/2:(-13)/3`

`x=1/2xx(-3)/13`

`x=(-3)/26`

___________________________

`3/4+1/4:x=2/5`

`1/4:x=2/5-3/4`

`1/4:x=8/20-15/20`

`1/4:x=(-7)/20`

`x=1/4:(-7)/20`

`x=1/4xx(-20)/7`

`x=(-5)/7`

`2/3 . x = (-5)/17`

`x= (-5)/17 : 2/3`

`x= (-5)/17 xx 3/2`

`x= (-5.3)/(17.2)`

`x=(-15)/34`

\(\dfrac{2}{3}.x=-\dfrac{5}{17}\)

\(x=-\dfrac{5}{17}:\dfrac{2}{3}\)

\(x=-\dfrac{5}{17}.\dfrac{3}{2}\)

\(x=-\dfrac{15}{34}\)

#Hphong2010

Ta có: \(\widehat{BOC}=\widehat{AOD}\) (`2` góc đối đỉnh)

  \(=>\widehat{AOD}=45^o \)

Lại có: \(\widehat{BOC}+\widehat{DOB}=180^o \) (`2` góc kề bù)

  \(=>45^o +\widehat{DOB}=180^o  \)

 \(=>\widehat{DOB}=135^o \)

 Mà \(\widehat{DOB}=\widehat{AOC}\) (`2` góc đối đỉnh)

  \(=>\widehat{AOC}=135^o \)

\(1-\dfrac{a}{a}=1-1=0\)

\(\Rightarrow\) \(1-\dfrac{a}{a}=0\)

#Hphong

`|x+3|+|x-2|=4`

Ta có bảng:

`@` Với `x < -3` ta có:

    `-x-3+2-x=0`

`=>-2x=1`

\(=>x=\dfrac{-1}{2}\) (ko t/m)

`@` Với \(-3 \le x < 2\) ta có:

    `x+3+2-x=0`

`=>0x=-5` (Vô lí)

`@` Với \(x \ge 2\) ta có:

    `x+3+x-2=0`

`=>2x=-1`

\(=>x=\dfrac{-1}{2}\) (ko t/m)

Vậy ko có gtr của `x` t/m.

\(\dfrac{x+2}{2021}+\dfrac{x+3}{2020}=\dfrac{x+2021}{2}+\dfrac{x+2020}{3}\)

\(=>\dfrac{x+2}{2021}+1+\dfrac{x+3}{2020}+1=\dfrac{x+2021}{2}+1+\dfrac{x+2020}{3}+1\)

\(=>\dfrac{x+2+2021}{2021}+\dfrac{x+3+2020}{2020}=\dfrac{x+2021+2}{2}+\dfrac{x+2020+3}{3}\)

\(=>\dfrac{x+2023}{2021}+\dfrac{x+2023}{2020}-\dfrac{x+2023}{2}-\dfrac{x+2023}{3}=0\)

\(=>(x+2023)(\dfrac{1}{2021}+\dfrac{1}{2020}-\dfrac{1}{2}-\dfrac{1}{3})=0\)

  Mà \(\dfrac{1}{2021}+\dfrac{1}{2020}-\dfrac{1}{2}-\dfrac{1}{3} \ne 0\)

  \(=>x+2023=0\)

 \(=>x=-2023\)

Thanks