28/56+3/5
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=\dfrac{-3}{5}+\dfrac{28}{5}\cdot\dfrac{9}{14}=\dfrac{-3}{5}+\dfrac{18}{5}=\dfrac{15}{5}=3\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có:56x2+28x5 +28
=28x2x2+28x5+28
=28x4+28x5+28
=28x(4+5+1)
=28x10=280
56 x 2 + 28 x 5 + 28
= 28 x 2 x 2 + 28 x 5 + 28 x 1
= 28 x 4 + 28 x 5 + 28 x 1
= 28 x ( 4 + 5 + 1 )
= 28 x 10
= 280
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{-3}{5}+\dfrac{28}{5}.\left(\dfrac{43}{56}+\dfrac{5}{24}-\dfrac{21}{63}\right)\)
= \(\dfrac{-3}{5}+\dfrac{28}{5}.\dfrac{9}{14}\)
= \(\dfrac{-3}{5}+\dfrac{28.9}{5.14}\)
= \(\dfrac{-3}{5}+\dfrac{18}{5}\)
= \(\dfrac{\left(-3\right)+18}{5}\)
= \(\dfrac{15}{5}=3\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) /-28/ + (-42) = 28 +(-42) = -14
b) đặt S = 76+75+74+73+72+7
7S = 7^7+7^6+7^5+7^4+7^3+7^2
7S-S= (7^7+7^6+7^5+7^4+7^3+7^2) - ( 76+75+74+73+72+7)
6S = 77-7 = 823536
S = 823536:6 =137256
140/280+168/280=308/280=11/10
140/280+168/280=308/280=11/10