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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) (-234) + |-145| + (-2019) + |155| + (-66)
= -234 + 145 - 2019 + 155 - 66
= (-234 - 66) + (145 + 155) - 2019
= -300 + 300 - 2019
= 0 - 2019 = -2019
b) -79.|-45| - 21.|45|
= -79.45 - 21.45
= (-79 - 21) . 45
= -100 . 45
= -4500
a, (-234) + |-145| + (-2019) + |155| + (-66)
= -234 + 145 - 2019 + 155 - 66
= (-234 - 66) + (145 + 155) - 2019
= -300 + 300 - 2019
= 0 - 2019
= -2019
b, -79 . |-45| - 21 . |45|
= -79 . 45 - 21 . 45
= 45 . ( -79 - 21 )
= 45 . (-100)
= -4500
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có:
\(12=2^2\cdot3\)
\(18=2\cdot3^2\)
\(75=3\cdot5^2\)
\(\Rightarrow BCNN\left(12,18,75\right)=2^2\cdot3^2\cdot5^2=900\)
\(\Rightarrow\)Phân số cần tìm là \(\frac{900}{45}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
F= 1/21+1/28+1/36+1/45+...+1/66
F/2=1/42+1/56+1/72+1/90+...+1/132
F/2=1/6.7+1/7.8+1/8.9+1/9.10+...+1/11.12
F/2=1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+...+1/11-1/12
F/2=1/6-1/12
F/2=1/12
F=1/12.2
F=1/6
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=\frac{4}{42}+\frac{4}{56}+\frac{4}{72}+\frac{4}{90}+\frac{4}{110}+\frac{4}{132}\)
\(=4.\left(\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}+\frac{1}{132}\right)\)
\(=4.\left(\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+...+\frac{1}{11.12}\right)\)
\(=4.\left(\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{11}-\frac{1}{12}\right)\)
\(=4.\left(\frac{1}{6}-\frac{1}{12}\right)\)
\(=4.\frac{1}{12}=\frac{4}{12}=\frac{1}{3}\)
olm k tôi đê
bị trừ bao nhiê điểm rồi
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
34.31+34.89+66:45
=34.(31+89)+66:45
=34.120+66:45
=4080+\(\frac{22}{15}\)
=\(\frac{61222}{15}\)
=4081,455557