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2155 - ( 174 + 2155) + (-68 + 174)
= 2155 - 2329 + 106
= -174 + 106
= -68
Ta có: 2155 - (174 + 2155) + (-68 + 174)
= 2155 - 174 - 2155 + (-68) + 174
= (2155 - 2155) - 174 + 174 + (-68)
= 0 + 0 + (-68)
= -68
![](https://rs.olm.vn/images/avt/0.png?1311)
2115 = (7.3)15 = 715.315
275.498 = (33)5.(72)8 = 315.716 = 7.315.715 > 315.715 = 2115
=> 275.498 > 2115.
![](https://rs.olm.vn/images/avt/0.png?1311)
2155 -(174+2155)+(-68+174)=2155 -174-2155+(-68)+174
=(2155-2155)+(-174+174)+-68
=-68
![](https://rs.olm.vn/images/avt/0.png?1311)
2155- (174 + 2155) + (- 68 +174)
=2155-174-2155-68+174
=(2155-2155)+(-174+174)-68
=0+0-68
=-68
= 2155 - 174 - 2155 - 68 +174
= ( 2155 - 2155) + ( -174 + 174) - 68
= 0+ 0 - 68
= -68
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
ta phải bỏ giấu (,) đi:
suy ra: =2155-174-2155-68+174
=(2155-2155)-(-174+174)-68
=0-0-68
=-68
![](https://rs.olm.vn/images/avt/0.png?1311)
1, 2155 -(174 + 2155) + (-68 + 174)
=2155 - 174 - 2155 -168 + 174
=(2155-2155)+(-174+174)-168
=-168
2, -25.72 + 25.21-49.25
=25.-72+25.21-49.25(vi -25.72=25.-72)
=25(-72+21-49)
=25.(-2)
=-50
![](https://rs.olm.vn/images/avt/0.png?1311)
a) C = 1/3 + 1/15 + ... + 1/2115
= 1/(1.3) + 1/(3.5) + ... + 1/(45.47)
= 1/2 . (1 - 1/3 + 1/3 - 1/5 + ... + 1/45 - 1/47}
= 1/2 . (1 - 1/47)
= 1/2 . 46/47
= 23/47
\(C=\dfrac{1}{3}+\dfrac{1}{15}+...+\dfrac{1}{2115}\\ \\ \\ \\ \\ C=\dfrac{1}{1.3}+\dfrac{1}{3.5}+\dfrac{1}{5.7}+...+\dfrac{1}{45.47}\\ \\ \\ \\ \\ \Rightarrow2C=\dfrac{2}{1.3}+\dfrac{2}{3.5}+\dfrac{2}{5.7}+...+\dfrac{2}{45.47}\\ \\ \\ \\ \\ 2C=\dfrac{1}{1}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{45}-\dfrac{1}{47}\\ \\ \\ \\ \\ 2C=\dfrac{1}{1}-\dfrac{1}{47}=\dfrac{46}{47}\\ \\ \\ \\ \\ \Rightarrow C=\dfrac{46}{47}:2\\ \\ \\ \\ \\ C=\dfrac{46}{47}\cdot\dfrac{1}{2}=\dfrac{23}{47}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(512.\left(2-128\right)-128.\left(-512\right)\)
\(=512.\left(-126\right)-128.\left(-512\right)\)
\(=\left(-512\right).126-128.\left(-512\right)\)
\(=\left(-512\right)\left(126-128\right)\)
\(=\left(-512\right).\left(-2\right)\)
\(=1024\)
b) \(2155-\left(174+2155\right)+\left(-68+174\right)\)
\(=2155-174-2155-68+174\)
\(=2155-2155-174+174-68\)
\(=-68\)
NĂM MỚI AN LÀNH
Ta có :
\(a)\)\(512.\left(2-128\right)-128.\left(-512\right)\)
\(=\)\(512\left(2-128+128\right)\)
\(=\)\(512.2\)
\(=\)\(1024\)
\(2115-\left(174+2115\right)+9\left(-68+174\right)\)
\(=2115-2289+9\left(-68+174\right)\)
\(=2115-2289+9.106\)
\(=-174+9.106\)
\(=-174+954\)
\(=780\)