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\(=-48+48\times\left(-78\right)+48\times\left(-21\right)\)
\(=48\times\left(-1-78-21\right)\)
\(=48\times\left(-100\right)\)
\(=-4800\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1}{2}+\frac{3}{4}=\frac{1.2}{2.2}+\frac{3}{4}=\frac{2}{4}+\frac{3}{4}=\frac{5}{4}\)
\(\frac{2}{-5}-\frac{-7}{9}=-\frac{2}{5}-\frac{-7}{9}=\frac{-2}{5}+\left(-\frac{7}{9}\right)=-\frac{18}{45}+-\frac{35}{45}=-\frac{53}{45}\)
cho kẹo~~~
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B= 1.99+2.98+2.97+...98.2+99.1
=1.99+2.(99-1)+3.(99-2)+...+98.(99-97)+99.(99-98)
=1.99+2.99-1.2+3.99-2.3+...+98.99-97.98+99.99-98.99
=(1.99+2.99+3.99+...+98.99+99.99)-(1.2+2.3+3.4+...+97.98+98.99)
=99.(1+2+3+...+98+99)-(1.2+2.3+3.4+...+97.98+98.99)
=99.4950-(1.2+2.3+3.4+...+97.98+98.99)
=490050-(1.2+2.3+3.4+...+97.98+98.99)
Đặt C=1.2+2.3+3.4+...+97.98+98.99
=> 3C=1.2.3+2.3.3+3.4.3+...+97.98.3+98.99.3
=1.2.3+2.3.(4-1)+...+98.99.(100-97)
=1.2.3+2.3.4-1.2.3+...+98.99.100-97.98.99
=98.99.100
=> A=(98.99.100):3=323400
Vậy B=490050-323400=166650
=1.99+2.(99-1)+3.(99-2)+4.(99-3)+......+99.(99-98)
=99.(1+2+3+.......+99)-(2+2.3+3.4+........+98.99)
=99.(1+99).99:2-98.99.100:3
=99.50.99-98.33.100
=490050-323400=166650
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=10080
tk mình.,mình kb rồi
=10080nhe
kb nha minh la nguyen van