\(2021^2-2021.4040+2020^2=2021^2-2.2021.2020+2020^2\)

\(=\left(2021-2020\right)^2=1^2=1\)

Tính nhanh

2020×28+74×2020-4040

= 2020 x 28 + 74 x 2020 - 2020 x 2

= 2020 x (28+74 - 2)

= 2020 x 100

= 202 000

Ta có: \(A=\frac{1}{1\cdot2}+\frac{1}{3\cdot4}+\cdots+\frac{1}{2021\cdot2022}\)

\(=1-\frac12+\frac13-\frac14+\cdots+\frac{1}{2021}-\frac{1}{2022}\)

\(=1+\frac12+\frac13+\frac14+\cdots+\frac{1}{2022}-2\left(\frac12+\frac14+\cdots+\frac{1}{2022}\right)\)

\(=1+\frac12+\frac13+\cdots+\frac{1}{2022}-1-\frac12-\cdots-\frac{1}{1011}\)

\(=\frac{1}{1012}+\frac{1}{1013}+\cdots+\frac{1}{2022}\)

Ta có: \(B=1011+\frac{1010}{1012}+\frac{1009}{1013}+\cdots+\frac{2}{2020}+\frac{1}{2021}\)

\(=\left(\frac{1010}{1012}+1\right)+\left(\frac{1009}{1013}+1\right)+\cdots+\left(\frac{2}{2020}+1\right)+\left(\frac{1}{2021}+1\right)+1\)

\(=\frac{2022}{1012}+\frac{2022}{1013}+\cdots+\frac{2022}{2022}=2022\left(\frac{1}{1012}+\frac{1}{1013}+\cdots+\frac{1}{2022}\right)\)

=2022A

=>\(\frac{B}{A}=2022\) là số nguyên

\(5x\left(x-2020\right)-2x+4040=0\)

\(\Rightarrow5x\left(x-2020\right)-2\left(x-2020\right)=0\)

\(\Rightarrow\left(x-2020\right)\left(5x-2\right)=0\)

\(\Rightarrow\left\{{}\begin{matrix}x-2020=0\\5x-2=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=2020\\x=\dfrac{2}{5}\end{matrix}\right.\)

Vậy....

\(PT< =>-|x+2020|+|x-2020|=4040\)(viết cho dễ nhìn)

Xét \(x< -2020\)thì tương đương với \(-x+2020+x+2020=4040\)

\(< =>4040=4040\)(thỏa mãn mọi x  > -2020)

Xét \(-2020\le x< 2020\)thì tương đương với \(-x+2020-x-2020=4040\)

\(< =>x=-\frac{4040}{2}=-2020\)(tmđk)

Xét \(x\ge2020\)thì tương đương với \(x-2020-x-2020=4040\)

\(< =>-4040=4040\)(vô lí)

Vậy ta có tập nghiệm \(x\le-2020\)thỏa mãn pt trên

làm xong tự nhiên ấn hủy :(( phải làm lại từ đầu

2020*14+4040*16+6060*18

= 1010*2*14+1010*4*16+1010*6*18

=1010*28+1010*64+1010*108

=1010*(28+64+108)

=1010*200=202000

= 2020 * 14 + 2020 * 2 * 16 + 2020 * 3 * 18

= 2020 * 14 + 2020 * 32 + 2020 * 54

=2020 * (14 + 32 + 54)

=2020 * 100

=20200

2020 x 14 + 4040 x 16 + 6060 x 18

= 2020 x 14 + 2020 x 2 x 16 + 2020 x 3 x 18

= 2020 x 14 + 2020 x 32 + 2020 x 54

= 2020 x (14 + 32 + 54)

= 2020 x 100

= 202000

\(2020\times14+4040\times16+6060\times18\)

\(=2020\times14+2020\times2\times16+2020\times3\times18\)

\(=2020\times14+2020\times32+2020\times54\)

\(=2020\times\left(14+32+54\right)\)

\(=2020\times100\)

\(=202000\)

27/-72 = 27:(-9)/-72:(-9) = -3/8

-2020:(-2020)/-4040:(-2020) = 1/2

11.8-11.3/17-6= 11.(8-3)/11= 11.5/11= 5

20-12.30/30+30.10 = 20-360/30+300 = -340/330 = -34/33 = -1 1/33

\(\text{#TuanNam}\)

`27/-72=-27/72=`\(\dfrac{-27\div9}{72\div9}=\dfrac{-3}{8}\) 

`-2020/-4040=202/404=`\(\dfrac{202\div202}{404\div202}=\dfrac{1}{2}\)

`11*8-`\(\dfrac{11\cdot3}{17-6}=88-3=85\) 

\(\dfrac{20-12\cdot20}{30+30\cdot10}=\dfrac{20\cdot\left(1-12\right)}{30\cdot\left(1+10\right)}=\dfrac{20\cdot-11}{30\cdot11}=-\dfrac{2}{3}\)