`Answer:`

\(1-2-3+4-5-6+7-8-9+...+2020-2021-2022\) (Mình sửa đề nhé.)

\(=\left(1-2-3\right)+\left(4-5-6\right)+\left(7-8-9\right)+...+\left(2020-2021-2022\right)\)

\(=\left(-4\right)+\left(-7\right)+\left(-10\right)+...+\left(-2023\right)\)

\(=[\left(2023-4\right):3+1].[\left(-2023-4\right):2]\)

\(=674.\left(-1013,5\right)\)

\(=-683099\)

`Answer:`

\(\frac{x+721}{2020}+\frac{x+21}{700}+\frac{x+721}{2021}=-1\) (Mình sửa đề nhé.)

\(\Leftrightarrow\frac{x+721}{2020}+\left(\frac{x+21}{700}+1\right)+\frac{x+721}{2021}=0\)

\(\Leftrightarrow\frac{x+721}{2020}+\left(\frac{x+21}{700}+\frac{700}{700}\right)+\frac{x+721}{2021}=0\)

\(\Leftrightarrow\frac{x+721}{2020}+\frac{x+21+700}{700}+\frac{x+721}{2021}=0\)

\(\Leftrightarrow\frac{x+721}{2020}+\frac{x+721}{700}+\frac{x+721}{2021}=0\)

\(\Leftrightarrow\left(x+721\right)\left(\frac{1}{2020}+\frac{1}{700}+\frac{1}{2021}\right)=0\)

Mà \(\frac{1}{2020}+\frac{1}{700}+\frac{1}{2021}\ne0\)

\(\Rightarrow x+721=0\Leftrightarrow x=-721\)

a,a, Mình vẽ ở dưới.

b,b, Ta áp dụng công thức: n(n−1)2=4(4−1)2=6n(n-1)2=4(4-1)2=6 đoạn thẳng.

c,c, Các đoạn thẳng: AB;BC;CD;AD;AC;BDAB;BC;CD;AD;AC;BD

=-9/23x( 5/8+3/8)

=9/23x8/8

=9/23x1

=9/23.

x= -5

y=8

z= 21

`Answer:`

Ta có: \(-\frac{4}{8}=\frac{x}{10}\)

\(\Leftrightarrow x.8=-4.10\)

\(\Leftrightarrow x.8=-40\)

\(\Leftrightarrow x=-40:8\)

\(\Leftrightarrow x=-5\)

Ta có: \(-\frac{4}{8}=-\frac{7}{y}\)

\(\Leftrightarrow-4y=-7.8\)

\(\Leftrightarrow-4y=-56\)

\(\Leftrightarrow y=-56:-4\)

\(\Leftrightarrow y=14\)

Ta có: \(-\frac{4}{8}=\frac{z}{-24}\)

\(\Leftrightarrow8z=-4.-24\)

\(\Leftrightarrow8z=96\)

\(\Leftrightarrow z=96:8\)

\(\Leftrightarrow z=12\)