= -103/273

= 0

= -5/7

5.\(-\dfrac{3}{7}+\dfrac{5}{13}+\dfrac{-4}{12}=-\dfrac{103}{273}\)

b.\(-\dfrac{5}{21}+\dfrac{-2}{21}+\dfrac{8}{24}=\dfrac{-5-2}{21}+\dfrac{8}{24}=-\dfrac{7}{21}+\dfrac{8}{24}=-\dfrac{1}{3}+\dfrac{8}{24}=0\)

c.\(\dfrac{5}{13}+\dfrac{-5}{7}+\dfrac{-20}{41}+\dfrac{8}{13}+\dfrac{-21}{41}=\left(\dfrac{5}{13}+\dfrac{8}{13}\right)+\left(\dfrac{-20}{41}+\dfrac{-21}{41}\right)+-\dfrac{5}{7}=1-1-\dfrac{5}{7}=-\dfrac{5}{7}\)

\(\dfrac{21}{24}\cdot\dfrac{2}{11}:\dfrac{9}{8}=\dfrac{21}{24}\cdot\dfrac{2}{11}\cdot\dfrac{8}{9}=\dfrac{16}{99}\)

\(\dfrac{17}{9}\cdot\dfrac{5}{6}:\dfrac{12}{13}=\dfrac{17}{9}\cdot\dfrac{5}{6}\cdot\dfrac{13}{12}=\dfrac{1105}{648}\)

a)\(\dfrac{14}{99}\)

b)\(\dfrac{1105}{648}\)

\(\dfrac{16}{99};\dfrac{1105}{648}\)

a. \(\left(\dfrac{-2}{7}+\dfrac{4}{7}\right)+\dfrac{1}{7}=\dfrac{2}{7}+\dfrac{1}{7}=\dfrac{3}{7}\)

b. \(\left(\dfrac{-8}{19}+\dfrac{27}{19}\right)+\left(\dfrac{-4}{21}+\dfrac{-17}{21}\right)+\dfrac{-12}{16}=\dfrac{19}{19}+\dfrac{-21}{21}+\dfrac{-12}{16}\)

\(=1+\left(-1\right)+\dfrac{-12}{16}=\dfrac{-12}{16}\)

c. \(\dfrac{-3}{7}+\dfrac{-11}{13}+\dfrac{-2}{13}+\dfrac{3}{7}+1=\left(\dfrac{-3}{7}+\dfrac{3}{7}\right)+\left(\dfrac{-11}{13}+\dfrac{-2}{13}\right)+1=0-1+1=0\)

a)-2/7+2/7:3/5

=

a)= -2/7 + 2/7 x 5/3                               c) = 6/5 x ( 3/13 - 16/13)
   = -2/7 + 10/27                                      = 6/5 x (-1)
   =  4/7                                                = -6/5
b) = (-8/19 + 27/19) + (-4/21 - 17/21) 
    = 1 + (-1)
    = 0
 

d) 

` (-3)/7 + 5/13 + (-4)/7 =   -3/7 + (-4/7 )  + 5/13 = -1 + 5/13 = -8/13`

e2) 

`-5/21 + (-2)/21 + (-8)/4 = -7/21 + -8/4 = -7/3`

\(6.-\dfrac{5}{18}=-\dfrac{5}{3}\)

\(-\dfrac{13}{24}+-\dfrac{5}{21}.\dfrac{7}{25}=-\dfrac{13}{24}+-\dfrac{1}{15}=-\dfrac{73}{120}\)

\(-\dfrac{5}{13}-\dfrac{3}{26}.-\dfrac{2}{3}=-\dfrac{5}{13}-\left(-\dfrac{1}{13}\right)=-\dfrac{4}{13}\)

\(\left(\dfrac{2}{3}+-\dfrac{7}{6}\right).\left(\dfrac{3}{8}+-\dfrac{3}{24}\right)=-\dfrac{1}{2}.\dfrac{1}{4}=\dfrac{1}{8}\)

Kết quả lần lượt của các phép tính là :

\(\dfrac{-5}{3}\) , \(\dfrac{-73}{120}\) , \(\dfrac{-4}{13}\) , \(\dfrac{-1}{8}\)

`# \text {DNamNgV}`

`16/21 + 6/7`

`= 16/21 + 18/21`

`= 34/21`

__

`15/22 \times 11/35`

`= (15 \times 11)/(22 \times 35)`

`= (5 \times 3 \times 11)/(2 \times 11 \times 5 \times 7)`

`= (3 \times 1)/(2 \times 7)`

`= 3/14`

___

`8/11 \div 5/22`

`= 8/11 \times 22/5`

`= (8 \times 22)/(11 \times 5)`

`= (8 \times 11 \times 2)/(11 \times 5)`

`= (8 \times 2)/5`

`= 16/5`

___

`9/13 \div 27/39`

`= 9/13 \times 39/27`

`= 9/13 \times 13/9`

`= 1`

a) \(\dfrac{23}{24}< 1\)

\(\dfrac{24}{23}>1\)

\(\Rightarrow\dfrac{23}{24}< \dfrac{24}{23}\)

b) \(\dfrac{4}{21}< \dfrac{4}{20}=\dfrac{1}{5}=\dfrac{6}{30}< \dfrac{6}{29}\)

c) \(\dfrac{6}{7}=1-\dfrac{1}{7}< \dfrac{8}{9}=1-\dfrac{1}{9}\)

d) \(\dfrac{1212}{1313}=\dfrac{12\times101}{13\times101}=\dfrac{12}{13}\)

Ta có: \(A=\dfrac{5}{13}+\dfrac{-5}{7}+\dfrac{-20}{41}+\dfrac{8}{13}+\dfrac{-21}{41}\)

\(=\left(\dfrac{5}{13}+\dfrac{8}{13}\right)+\left(\dfrac{-20}{41}+\dfrac{-21}{41}\right)+\dfrac{-5}{7}\)

\(=1-1+\dfrac{-5}{7}\)

\(=\dfrac{-5}{7}\)

Có 2 dấu = hả bạn

\(A=\dfrac{5}{13}+\dfrac{-5}{7}+\dfrac{-20}{41}+\dfrac{8}{13}+\dfrac{-21}{41}=(\dfrac{5}{13}+\dfrac{8}{13})+(\dfrac{-20}{41}+\dfrac{-21}{41})+(\dfrac{-5}{7})=1+\left(-1\right)+\dfrac{-5}{7}=0+\dfrac{-5}{7}=\dfrac{-5}{7}\)

bài 2:tính hợp lý

1.a) Dễ nhận thấy đề toán chỉ giải được khi đề là tìm x,y. Còn nếu là tìm x ta nhận thấy ngay vô nghiệm. Do đó: Sửa đề: \(\left|x-3\right|+\left|2-y\right|=0\)

\(\Leftrightarrow\left|x-3\right|=\left|2-y\right|=0\)

\(\left|x-3\right|=0\Rightarrow\left\{{}\begin{matrix}x-3=0\\-\left(x-3\right)=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=3\\x=-3\end{matrix}\right.\) (1)

\(\left|2-y\right|=0\Rightarrow\left\{{}\begin{matrix}2-y=0\\-\left(2-y\right)=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=2\\y=-2\end{matrix}\right.\) (2)

Từ (1) và (2) có: \(\left[{}\begin{matrix}\left\{{}\begin{matrix}x_1=3\\x_2=-3\end{matrix}\right.\\\left\{{}\begin{matrix}y_1=2\\y_2=-2\end{matrix}\right.\end{matrix}\right.\)

Bài 2: 

a: \(=\dfrac{-6\left(\dfrac{1}{7}-\dfrac{1}{13}+\dfrac{1}{29}\right)}{9\left(\dfrac{1}{7}-\dfrac{1}{13}+\dfrac{1}{29}\right)}=\dfrac{-6}{9}=\dfrac{-2}{3}\)

b: \(=\dfrac{\dfrac{2}{15}-\dfrac{2}{21}+\dfrac{2}{39}}{\dfrac{10}{40}-\dfrac{10}{56}+\dfrac{10}{104}}\)

\(=\dfrac{\dfrac{2}{3}\left(\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{13}\right)}{\dfrac{10}{8}\left(\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{13}\right)}=\dfrac{2}{3}:\dfrac{5}{4}=\dfrac{2}{3}\cdot\dfrac{4}{5}=\dfrac{8}{15}\)

c: \(=\dfrac{2\left(25-\dfrac{2}{13}+\dfrac{1}{15}-\dfrac{1}{17}\right)}{4\left(25-\dfrac{2}{13}+\dfrac{1}{15}-\dfrac{1}{17}\right)}:\dfrac{1+\dfrac{2}{21}-\dfrac{5}{121}}{13\left(\dfrac{5}{121}-\dfrac{2}{21}-1\right)}\)

=2/4:(-1)/13=2/4x(-13)=-13/2