Bài 1: 

a: -8/12<0<-3/-4

b: -56/24<0<7/3

c: 4/25<1<15/13

=>-4/25>-15/13

Bài 2: 

a: =-60/45=-4/3

b: =4/15-3/2-8/5=8/30-45/30-48/30=-85/30=-17/6

cần gấp

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     Giải :

\(B=\left[\left(-\frac{3}{7}\right)^5\right]^4\)

\(B=\left(-\frac{3}{7}\right)^{20}\)

\(A=\frac{3}{7}\cdot\left(\frac{3}{7}\right)^{19}\)

\(A=\left(\frac{3}{7}\right)^{20}\)

\(\Rightarrow A>B\)

           [ hoq chắc ]

a: 3/5>-19/5

b: 8/7<8/3

c: 3/4=15/20

2/5=8/20

mà 15>8

nên 3/4>2/5

d: -3/5=-18/30

-4/6=-20/30

mà -18>-20

nên -3/5>-4/6

a: 3/5>-19/5

b: 8/7<8/3

c: 3/4=15/20

2/5=8/20

mà 15>8

nên 3/4>2/5

d: -3/5=-18/30

-4/6=-20/30

mà -18>-20

nên -3/5>-4/6

a) Ta có:

\(A=\dfrac{-68}{123}\cdot\dfrac{-23}{79}=\dfrac{68}{123}\cdot\dfrac{23}{79}\)

\(B=\dfrac{-14}{79}\cdot\dfrac{-68}{7}\cdot\dfrac{-46}{123}=-\left(\dfrac{14}{79}\cdot\dfrac{68}{7}\cdot\dfrac{46}{123}\right)\)

\(C=\dfrac{-4}{19}\cdot\dfrac{-3}{19}\cdot...\cdot\dfrac{0}{19}\cdot...\cdot\dfrac{3}{19}\cdot\dfrac{4}{19}=0\)

Suy ra A là số hữu tỉ dương, B là số hữu tỉ âm và C là 0.

Vậy A > C > B.

b) Ta có:

\(\dfrac{B}{A}=\dfrac{-\left(\dfrac{14}{79}\cdot\dfrac{68}{7}\cdot\dfrac{46}{123}\right)}{\dfrac{68}{123}\cdot\dfrac{23}{79}}=-\dfrac{14}{79}\cdot\dfrac{68}{7}\cdot\dfrac{46}{123}\cdot\dfrac{123}{68}\cdot\dfrac{79}{23}\)

\(\dfrac{B}{A}=-\dfrac{14\cdot68\cdot46\cdot123\cdot79}{79\cdot7\cdot123\cdot68\cdot23}=-\left(2\cdot2\right)=-4\)

Vậy B : A = -4

\(-\frac{3}{7}.\frac{5}{9}+\frac{4}{9}.\frac{-3}{7}+2.\frac{3}{7}\)\(=\frac{3}{7}\left(-\frac{5}{9}-\frac{4}{9}+2\right)=\frac{3}{7}\left(-1+2\right)=\frac{3}{7}\)

so sánh: \(\frac{21}{-42}=\frac{1}{-2}=\frac{2}{-4}\); vì \(\frac{2}{-4}>\frac{3}{-4}\)nên \(\frac{21}{-42}>\frac{3}{-4}\)

tìm x: a) \(x-\frac{2}{5}=\frac{1}{10}\)

             \(\Rightarrow x=\frac{1}{10}+\frac{2}{5}=\frac{1}{10}+\frac{4}{10}=\frac{5}{10}=\frac{1}{2}\)

b) \(\frac{4}{6}+\frac{5}{4}x=\frac{7}{6}\)

\(\Rightarrow\frac{5}{4}x=\frac{3}{6}=\frac{1}{2}\)

\(\Rightarrow x=\frac{2}{5}\)

a) 7.x - x = 5²¹ : 5¹⁹ + 3.2² - 7⁰

6x = 25 + 12 - 1

6x = 36

x = 6

b) 7x - 2x = 6¹⁷ : 6¹⁵ + 44 : 11

5x = 36 + 4

5x = 40

x = 8

c) 5x + x = 39 - 3¹¹ : 3⁹

6x = 39 - 9

6x = 30

x = 5

d) [(6x - 39) : 7]. 4 = 12

(6x - 39) : 7 = 12 : 4

(6x - 39) : 7 = 3

6x - 39 = 3 . 7

6x - 39 = 21

6x = 21 + 39

6x = 60

x = 10

x =