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`1 - 2 + 3 - 4 + 5 - 6 +...+ 2021 - 2022`
`= (1 - 2) + (3 - 4) + (5 - 6) +...+ (2021 - 2022)`
`= (-1) + (-1) + (-1) + ... + (-1) ` [có `2022 : 2 = 1011` nhóm]
`= (-1) xx 1011 = -1011`
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(\left(29,42+20,58\right)-\left(34,23+25,77\right)\)
\(=50-60=-10\)
b) \(-\left(212,49+87,51\right)+99,9\)
\(=-300+99,9=-200,1\)
A)29.42+20.58−34.23+(−25.77)29.42+20.58−34.23+(−25.77)
=29.42+20.58−34.23−25.77
=29.42+20.58−34.23−25.77
=(29.42+20.58)−(34.23+25.77)
=(29.42+20.58)−(34.23+25.77)
=50−60=50−60
=−10=−10
B).(−212.49)−(87.51−99.9)(−212.49)−(87.51−99.9)
=−212.49−87.51+99.9
=−212.49−87.51+99.9
=−(212.49+87.51)+99.9
=−(212.49+87.51)+99.9
=−300+99.9=−300+99.9
=−(300−99.9)=−(300−99.9)
=−200.1
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a: \(232-\left(581+132-331\right)\)
\(=232-581-132+331\)
\(=\left(232-132\right)+\left(-581+331\right)\)
\(=100-250\)
=-150
b: \(\left[12+\left(-57\right)\right]-\left[-57-\left(-12\right)\right]\)
\(=12+\left(-57\right)+57+\left(-12\right)\)
\(=\left(12-12\right)+\left(57-57\right)\)
=0+0
=0
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\(\dfrac{1}{2}\cdot1\cdot\dfrac{1}{3}\cdot10\cdot\dfrac{7}{35}\cdot\dfrac{3}{4}\)
\(=\dfrac{1}{2}\cdot10\cdot\dfrac{1}{5}\cdot1\cdot\dfrac{1}{3}\cdot\dfrac{3}{4}\)
\(=\dfrac{10}{10}\cdot\dfrac{1}{4}=\dfrac{1}{4}\)
\(\frac{45.86+45.15-45}{50.37-50.5+50.58}\)
\(=\frac{45.\left(86+15-1\right)}{50.\left(37-5+58\right)}\)
\(=\frac{45.100}{50.90}\)
\(=1\)
học tốt
A = \(\frac{45x\left(86+15-1\right)}{50x\left(37-5+58\right)}\)
A=\(\frac{45x100}{50x90}\)= \(\frac{2}{2}\)= 1
(Cái phần cuối thì bạn rút họn 45 với 90, 50 với 100)