\(A=\frac{1}{2}+\frac{1}{14}+\frac{1}{35}+\frac{1}{65}+\frac{1}{104}+\frac{1}{152}=>\frac{1}{2}A=\frac{1}{4}+\frac{1}{28}+\frac{1}{70}+...+\frac{1}{304}\)

                                                                                                   \(=\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.10}+...+\frac{1}{16.19}=\frac{1}{3}.\left(\frac{3}{1.4}+\frac{3}{4.7}+...+\frac{3}{16.19}\right)=\frac{1}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{16}-\frac{1}{19}\right)=\frac{1}{3}.\left(1-\frac{1}{19}\right)=\frac{1}{3}.\frac{18}{19}=\frac{6}{19}\)=> A= \(\frac{6}{19}:\frac{1}{2}=\frac{12}{19}\)

đúng nha

A=2/4+2/28+2/70+2/130+2/208+2/304

A=2/1.4+2/4.7+2/7.10+2/10.13+2/13.16+2/16.19

A=2/3.(1-1/4+1/4-1/7+...+1/16-1/19)

A=2/3.(1-1/19)

A=2/3.18/19

A=12/19

Cách này nhanh hơn nhưng vẫn đúng bạn ạ

1.

\(35\times\left(14-23\right)-23\times\left(14-35\right)\)

\(=35\times14-35\times23-23\times14+23\times35\)

\(=\left(23\times35-35\times23\right)+14\times\left(35-23\right)\)

\(=0+14\times12\)

\(=168\)

2.

\(27\times\left(13-16\right)-16\times\left(13-27\right)\)

\(=27\times13-27\times16-16\times13+16\times27\)

\(=13\times\left(27-16\right)+\left(27\times16-16\times27\right)\)

\(=13\times11+0\)

\(=143\)

3.

\(44\times\left(-36\right)+22\times\left(-28\right)\)

\(=22\times2\times\left(-36\right)+22\times\left(-28\right)\)

\(=22\times\left(-72\right)+22\times\left(-28\right)\)

\(=22\times\left[\left(-72\right)+\left(-28\right)\right]\)

\(=22\times\left(-100\right)\)

\(=-2200\)

Chúc bạn học tốt

Tách ít ra thôi bn.

Tách ít ra thôi bn.

8: =156x200=31200

10: =-1945-567+1945=-567

1) 2155 - (174 + 2155) + (-68 + 174)

=2155-174-2155-68+174

=(2155-2155)+(-174+174)-68

=0+0-68

=-68

2) -25 . 72 + 25 . 21 - 49 . 25

=25.(-72+21-49)

=25.(-100)

=-2500

3) 35(14 - 23) - 23(14 - 35)

=35.(-9)-23.(-21)

=(-315)-(-483)

=168

4) 8154 - (674 + 8154) + (-98 + 674)

= 8154-674-8154-98+674

=(8154-8154) + (-674+674) - 98

=0+0-98

=-98

1) 68

2) -2500

3)-88

4)-98

lấy máy tính mà tính

hihi

a: =8/20-5/20+6/20=9/20

b: =-2/5:9/10=-2/5*10/9=-20/45=-4/9

c: =7/8*4/9+1/14*14/5

=28/72+1/5

=53/90

d: =2/7(3/11+8/11)

=2/7

tách ra đi 

Bài 1 : Tính

a) (-14) + (-28) = -42

b) (-26) + 47 = 21

c) 35 + (-63) = -28

d) (-8) + 12 + (-24) = -(8 + 24) + 12 =  -32 + 12 = -20

e) (-26) - 27 = -53

f) (-35) - ( 105) [ Tôi không biết làm :v ]

Bài 2 :

a) 54 + (12 + 46) = 54 + 12 + 46 = 54 + 46 + 12 = 100 + 12 = 112

b) 157 - ( 200 + 57 ) = 157 - 200 + 57 = 157 - 57 - 200 = -100

Còn lại tự tính :v

mik chỉ làm bài 1 thôi nha  bài bạn gửi dài quá

^{_{Bài 1 : Tính}}

^{_{a) (-14) + (-28) = -42}}

^{_{b) (-26) + 47 = 21}}

^{_{c) 35 + (-63) = -28}}

^{_{d) (-8) + 12 + (-24) = -(8 + 24) + 12 =  -32 + 12 = -20}}

^{_{e) (-26) - 27 = -53}}

^{_{f) (-35) - ( 105) =-140}}

Bài 1: Tính 

a) (−14) + (− 28) = -42                b) ( −26) + 47= 21          c) 35 + (− 63) = -28                                        

d) ( −8) +12 +( −24)= -20            e) ( −26)−27= -53           f) ( −35)− ( −105)=70  

Bài 2: Tính hợp lý 

a) 54 +(12+ 46)= 112          b) 157− (200+57) =-100                 

 c) (− 34) [(− 34)+2020]=(-34)+1986=1952   

d) 45− (137− 155)=63   e) 27− 8− 12− 7 =0                 

 f) ( −72)+26 −28− 6 =-80 

a) \(\frac{{ - 3}}{7}.\frac{2}{5} + \frac{2}{5}.\left( { - \frac{5}{{14}}} \right) - \frac{{18}}{{35}}\)

\(\begin{array}{l} = \frac{2}{5}.\left( {\frac{{ - 3}}{7} + \frac{{ - 5}}{{14}}} \right) - \frac{{18}}{{35}}\\ = \frac{2}{5}.\left( {\frac{{ - 6}}{{14}} + \frac{{ - 5}}{{14}}} \right) - \frac{{18}}{{35}}\\ = \frac{2}{5}.\frac{{ - 11}}{{14}} - \frac{{18}}{{35}} = \frac{{ - 11}}{{35}} - \frac{{18}}{{35}} =  \frac{{ -29}}{{35}}\end{array}\)

b) \(\left( {\frac{2}{3} - \frac{5}{{11}} + \frac{1}{4}} \right):\left( {1 + \frac{5}{{12}} - \frac{7}{{11}}} \right)\)

\(\begin{array}{l} = \left( {\frac{{2.11.4}}{{3.11.4}} - \frac{{5.3.4}}{{11.3.4}} + \frac{{1.3.11}}{{4.3.11}}} \right):\left( {\frac{11.12}{11.12} + \frac{{5.11}}{{12.11}} - \frac{{7.12}}{{11.12}}} \right)\\ = \left( {\frac{{88 - 60 + 33}}{{121}}} \right):\left( { \frac{{121+55 - 84}}{{121}}} \right)\\ = \frac{{61}}{{121}}:\frac{{92}}{{121}} = \frac{{61}}{{121}}.\frac{{121}}{{92}}= \frac{{61}}{{92}}\end{array}\)

c) \(\left( {13,6 - 37,8} \right).\left( { - 3,2} \right)\)

\( = \left( { - 24,2} \right).\left( { - 3,2} \right) = 77,44\)

d) \(\left( { - 25,4} \right).\left( {18,5 + 43,6 - 16,8} \right):12,7\)

\(\begin{array}{l} = \left( { - 25,4} \right).\left( {62,1 - 16,8} \right):12,7\\ = \left( { - 25,4} \right).45,3:12,7\\ = \left( { - 25,4} \right):12,7.45,3\\ =  (- 2).45,3 =  - 90,6\end{array}\)

a: \(=\dfrac{2}{5}\cdot\left(-\dfrac{3}{7}-\dfrac{5}{14}\right)-\dfrac{18}{35}\)

\(=\dfrac{2}{5}\cdot\dfrac{-6-5}{14}-\dfrac{18}{35}\)

\(=\dfrac{2}{5}\cdot\dfrac{-11}{14}-\dfrac{18}{35}=-\dfrac{22}{70}-\dfrac{18}{35}=\dfrac{-58}{70}=-\dfrac{29}{35}\)

b: \(=\dfrac{88-60+33}{132}:\dfrac{132+55-84}{132}\)

\(=\dfrac{61}{132}\cdot\dfrac{132}{103}=\dfrac{61}{103}\)

c: \(=-24.2\cdot\left(-3.2\right)=24.2\cdot3.2=77.44\)

d: \(=\dfrac{-25.4}{12.7}\cdot45.3=-2\cdot45.3=-90.6\)