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`D = 2000 - 1999 + 1998 -1997 + ... + 2 - 1`
`D = (2000-1999)+(1998-1997)+...+(2-1)`
`D = 1+1+...+1`
Ta có: `(2000-1) \div 1 + 1 = 1000`
`\rightarrow` Có `1000` hiệu tương tự
`\rightarrow` `D= 1+1+...+1 = 1000.`
Để ý: 2000 - 1999= 1
1998-1997=1
....
2-1=1
Có 1000 hiệu như vậy
D = 1000
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Ta có \(B=\left(1-\dfrac{1}{2}\right)\left(1-\dfrac{1}{3}\right)\left(1-\dfrac{1}{4}\right)...\left(1-\dfrac{1}{2021}\right)\left(1-\dfrac{1}{2022}\right)\)
\(B=\dfrac{1}{2}.\dfrac{2}{3}.\dfrac{3}{4}...\dfrac{2020}{2021}.\dfrac{2021}{2022}\)
\(B=\dfrac{1}{2022}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(B=1-\dfrac{3}{1\cdot4}-\dfrac{3}{4\cdot7}-...-\dfrac{3}{2020\cdot2023}\\ =1-\left(\dfrac{3}{1\cdot4}+\dfrac{3}{4\cdot7}+...+\dfrac{3}{2020\cdot2023}\right)\\ =1-\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{2020}-\dfrac{1}{2023}\right)\\ =1-\left(1-\dfrac{1}{2023}\right)\\ =1-\dfrac{2022}{2023}=\dfrac{1}{2023}\)
`B=1-3/(1.4)-3/(4.7)-3/(7.10)-....-3/(2020.2023)`
`B=1-(3/(1.4)+3/(4.7)+.....+3/(2020.2023))`
`B=1-(1-1/4+1/4-1/7+.....+1/2020-1/2023)`
`B=1-(1-1/2023)`
`B=1-1+1/2023=1/2023`
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B = 1/6 + 1/12 + 1/20 + ... + 1/90
B = 1/2.3 + 1/3.4 + 1/4.5 + ... + 1/9.10
B = 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + ... + 1/9 - 1/10
B = 1/2 - 1/10
B = 5/10 - 1/10
B = 4/10 = 2/5
Ủng hộ mk nha ♡_♡☆_☆
![](https://rs.olm.vn/images/avt/0.png?1311)
\(B=\dfrac{1}{2}\cdot\dfrac{2}{3}\cdot...\cdot\dfrac{2020}{2021}\cdot\dfrac{2021}{2022}=\dfrac{1}{2022}\)
\(B=\left(1-\dfrac{1}{2}\right)\cdot\left(1-\dfrac{1}{3}\right)\cdot\left(1-\dfrac{1}{4}\right)\cdot\cdot\cdot\left(1-\dfrac{1}{2021}\right)\cdot\left(1-\dfrac{1}{2022}\right)\)
\(B=\left(\dfrac{2}{2}-\dfrac{1}{2}\right)\cdot\left(\dfrac{3}{3}-\dfrac{1}{3}\right)\cdot\left(\dfrac{4}{4}-\dfrac{1}{4}\right)\cdot\cdot\cdot\left(\dfrac{2021}{2021}-\dfrac{1}{2021}\right)\cdot\left(\dfrac{2022}{2022}-\dfrac{1}{2022}\right)\)
\(B=\dfrac{1}{2}\cdot\dfrac{2}{3}\cdot\dfrac{3}{4}\cdot\cdot\cdot\dfrac{2020}{2021}\cdot\dfrac{2021}{2022}\)
\(B=\dfrac{1\cdot2\cdot3\cdot\cdot\cdot2020\cdot2021}{2\cdot3\cdot4\cdot\cdot\cdot2021\cdot2022}\)
\(B=\dfrac{1}{2022}\)
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B=x-y-(-18)=x-y+18
Khi x=-40 và y=-54 thì \(B=-40-\left(-54\right)+18\)
\(=-40+54+18\)
=14+18
=32
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1, S1 = (-2) + (-2) +..+ (-2).
Có SS (-2) là :
(1997 - 1) : 4 +1 = 500 (số ).
Tổng số (-2) là: 500 x (-2) = (-1000)
Bạn chờ mình làm tiếp nha
Các bạn ơi làm giúp mình vs ạ,mình đang cần gấp lắm rồi!!!!HELP MEEEEEEEEEEEEEE