18/49

20/7

14/11

3/35

1. \(-\dfrac{1}{5}-\left(-\dfrac{2}{3}\right)=\dfrac{-1}{5}+\dfrac{2}{3}=\dfrac{7}{15}.\)

2. \(-\dfrac{2}{5}-\dfrac{1}{7}=\dfrac{-14-5}{35}=\dfrac{-19}{35}.\)

3. \(\dfrac{3}{5}-\dfrac{5}{7}=\dfrac{21-25}{35}=\dfrac{-4}{35}.\)

4. \(\dfrac{4}{7}+\dfrac{-5}{8}-\dfrac{3}{28}=\dfrac{32-35-6}{56}=\dfrac{-9}{56}.\)

1: \(=\dfrac{-1}{5}+\dfrac{2}{3}=\dfrac{-3+10}{15}=\dfrac{7}{15}\)

2: \(=\dfrac{-14}{35}-\dfrac{5}{35}=-\dfrac{19}{35}\)

3: \(=\dfrac{21}{35}-\dfrac{25}{35}=-\dfrac{4}{35}\)

4: \(=\dfrac{32}{56}-\dfrac{35}{56}-\dfrac{6}{56}=\dfrac{-9}{56}\)

a >

b <

c >

d <

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\(a:ta.c\text{ó}:BCNN:12\\ \dfrac{2}{3}=\dfrac{2\cdot4}{3\cdot4}=\dfrac{8}{12};\dfrac{1}{4}=\dfrac{1\cdot3}{4\cdot3}=\dfrac{3}{12}\\ v\text{ì }\dfrac{8}{12}< \dfrac{3}{12}n\text{ê}n\dfrac{2}{3}< \dfrac{1}{4}\\ b:ta.c\text{ó}:\\ 10=2\cdot5\\ 8=2^3\\ \Rightarrow BCNN=2^3\cdot5=8\cdot5=40\\ \dfrac{7}{10}=\dfrac{7\cdot4}{10\cdot4}=\dfrac{28}{40};\dfrac{7}{8}=\dfrac{7\cdot5}{8\cdot5}=\dfrac{35}{40}\\ v\text{ì }\dfrac{28}{40}< \dfrac{35}{40}n\text{ê}n\dfrac{7}{10}< \dfrac{7}{8}\\ c:ta.c\text{ó}:\\ 7=7;5=5\\ \Rightarrow BCNN=7\cdot5=35\\ \dfrac{6}{7}=\dfrac{6\cdot5}{7\cdot5}=\dfrac{30}{35};\dfrac{3}{5}=\dfrac{3\cdot7}{5\cdot7}=\dfrac{21}{35}\\ v\text{ì }\dfrac{30}{35}>\dfrac{21}{35}n\text{ê}n\dfrac{6}{7}>\dfrac{3}{5}\\ d:ta.c\text{ó}:\\ 21=3\cdot7\\ 72=2^3\cdot3^2\\ \Rightarrow BCNN=2^3\cdot3^2\cdot7=504\\ \dfrac{14}{21}=\dfrac{14\cdot24}{21\cdot24}=\dfrac{336}{504};\dfrac{60}{72}=\dfrac{60\cdot7}{72\cdot7}=\dfrac{420}{504}\\ v\text{ì }\dfrac{336}{504}< \dfrac{420}{504}n\text{ê}n\dfrac{14}{21}< \dfrac{60}{72}\)

đề thiếu bạn ơi

hoặc đề sai

..............

bn viết thiếu đề nhé

A= 71 + 72 + 73 + 74 = (71+74)+(72+73) = 145 + 145 = 290 chia hết cho 5

=> A=........ chia hết cho 5

B=  10⁶-5⁷ = 2⁶. 5⁶ - 5⁷ = 5⁶ ( 2⁶ - 5) =(5⁶ . 59) chia hết cho 59 => B chia hết cho 59

A bn viết thiếu chỗ 7 => 71 đấy

1: \(=-\dfrac{3}{4}+3-\dfrac{1}{4}-\dfrac{5}{4}+\dfrac{9}{2}=-\dfrac{9}{4}+3+\dfrac{9}{2}=\dfrac{-9+12+18}{4}=\dfrac{21}{4}\)

2: \(=\dfrac{-5}{7}\left(\dfrac{13}{19}+\dfrac{6}{19}\right)+\dfrac{5}{7}=\dfrac{-5}{7}+\dfrac{5}{7}=0\)

3: \(=\dfrac{2}{5}\left(1-\dfrac{8}{3}-\dfrac{5}{8}\right)=\dfrac{2}{5}\cdot\dfrac{-55}{24}=\dfrac{-11}{12}\)

câu này để mình bày cho

ơ...... mình không biết

F = 7 + 72 + 73 + 74 + ..... + 7100 

F= 7+(1+7)+73+(1+7)+...+799+(1+7)

F = 7x8+73x8+...+799x8

F= 8x(7+73+...+799)

mà 8 chia hết 8 => 8(7+73+...+799) chia hết 8

Vậy F chia hết cho 8

2)

\(F=7+7^2+7^3+7^4+...+7^{100}\\ F=7\cdot\left(1+7\right)+7^3\cdot\left(1+7\right)+.....+7^{99}\cdot\left(1+7\right)\\F=7\cdot8+7^3\cdot8+.....+7^{99}\cdot8\\ F=8\cdot\left(7+7^3+....+7^{99}\right)\\ =>F⋮8\) 

Tick giúp mik với

1: Ta có: 7x+6(3-x)=27-20+73

\(\Leftrightarrow7x+18-6x=80\)

\(\Leftrightarrow x=80-18=62\)

Vậy: x=62

2: Ta có: \(6x-5\left(x-7\right)=\left(27-514\right)-486-73\)

\(\Leftrightarrow6x-5x+35=27-514-486-73\)

\(\Leftrightarrow x+35=-1046\)

\(\Leftrightarrow x=-1081\)

Vậy: x=-1081