=0 nha

Ta có: 

\(\frac{2021}{1}+\frac{2020}{2}+\frac{2019}{3}+...+\frac{2}{2020}+\frac{1}{2021}\)

\(=1+\frac{2020}{2}+1+\frac{2019}{3}+...+1+\frac{2}{2020}+1+\frac{1}{2021}+1\)

\(=\frac{2022}{2}+\frac{2022}{3}+...+\frac{2022}{2020}+\frac{2022}{2021}+\frac{2022}{2022}\)

\(=2022\left(\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2020}+\frac{1}{2021}+\frac{1}{2022}\right)\)

Do đó giá trị của \(M\)là: 

\(M=\frac{2022\left(\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2020}+\frac{1}{2021}+\frac{1}{2022}\right)}{\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2020}+\frac{1}{2021}+\frac{1}{2022}}=2022\)

            2021/1 + 2/2020 + 2019/3 + ... + 2/2020 + 1/2021

M    =       _______________________________________

                    1/2 + 1/3 + ... + 1/2020 + 1/2021 + 1/2022

=\(\frac{2022+\frac{2022}{2}+...+\frac{2022}{2021}-2021}{\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2022}}=\frac{1+\frac{2022}{2}+...+\frac{2022}{2021}}{\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2022}}\)

=2022

(3+6+9+12+15+18+21)-x=13

84-x=13

x=71

#H

( 3 + 6 + 9 + 12 + 15 + 18 + 21 ) - x = 13

                                                 84-x =13

                                                      x =84-13

                                                      x =74

                           k nha

đề bài là tính j bạn

Mik quên mất, Đề là tính giá trị biểu thức và đó là câu c

c)\(1-\left(x-\frac{1}{5}\right)^2=\frac{21}{25}\)

\(\Leftrightarrow\left(x-\frac{1}{5}\right)^2=\frac{4}{25}\)

\(\Leftrightarrow x-\frac{1}{5}=\frac{2}{5}\)

\(\Leftrightarrow x=\frac{3}{5}\)

d)\(\left|x+\frac{1}{3}\right|.3\frac{2}{5}=\frac{2}{5}\)

\(\Leftrightarrow\left|x+\frac{1}{3}\right|.\frac{17}{5}=\frac{2}{5}\)

\(\Leftrightarrow\left|x+\frac{1}{3}\right|=\frac{2}{17}\)

\(\Leftrightarrow\orbr{\begin{cases}x+\frac{1}{3}=\frac{2}{17}\\x+\frac{1}{3}=-\frac{2}{17}\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-\frac{11}{51}\\x=-\frac{23}{51}\end{cases}}}\)

#H

1-(x-1/5)²=21/25

   (x-1/5)²=1-21/25

   (x-1/5)²=4/25

   (x-1/5)²=(2/5)²

       x-1/5=2/5

             x=2/5+1/5

             x=3/5

k nha

123.123

=15129

#H

123.123= 15129

ko chắc lắm nha

ai chên 10 k mình nha

 a) 3126+985

=4111

  958+3126

=4084

3126+985=4201

958+3126=4201

Thấy đúng k cho tui

 4x+5x-x=128

x(4+5-1)=128

x.8=128

x=16

\(\frac{x-1}{x+2}=\frac{x-2}{x+3}\)

\(\Leftrightarrow\left(x-1\right)\left(x+3\right)=\left(x+2\right)\left(x-2\right)\)

\(\Leftrightarrow x^2+2x-3=x^2-4\)

\(\Leftrightarrow2x-3=-4\)

\(\Leftrightarrow2x=-1\)

\(\Leftrightarrow x=\frac{-1}{2}\)

Vậy x = -1/2