Bài 1:

1)mik ko biết trục số ở đâu nên tham khảo:

2

-0,75 <5/3

a: -3/100=-9/300; -2/3=-200/300

=>-3/100>-2/3

b: -3/5=-9/15

-2/3=-10/15

=>-3/5>-2/3

c: -5/4<-1<-3/8

d: -2/3=-8/12; -3/4=-9/12

=>-2/3>-3/4

e: -267/268>-1

-1>-1347/1343

=>-267/268>-1347/1343

Lời giải:
a. $\frac{3}{-7}=\frac{-27}{63}$

$\frac{-5}{9}=\frac{-35}{63}$

Do $\frac{27}{63}< \frac{35}{63}$ nên $\frac{-27}{63}> \frac{-35}{63}$

$\Rightarrow \frac{3}{-7}> \frac{-5}{9}$

---------

b.

$-0,625=\frac{-625}{1000}=\frac{-5}{8}=\frac{-125}{200}$

$\frac{-19}{50}=\frac{-76}{200}> \frac{-125}{200}$

$\Rightarrow -0,625> \frac{-19}{50}$

c.

$-2\frac{5}{9}=-(2+\frac{5}{9})=\frac{-23}{9}=-(\frac{-23}{-9})$

-11>-78

nên \(-\dfrac{11}{3^7\cdot7^4}>-\dfrac{78}{3^7\cdot7^4}\)

1: B là số nguyên

=>n-3 thuộc {1;-1;5;-5}

=>n thuộc {4;2;8;-2}

3:

a: -72/90=-4/5
b: 25*11/22*35

\(=\dfrac{25}{35}\cdot\dfrac{11}{22}=\dfrac{5}{7}\cdot\dfrac{1}{2}=\dfrac{5}{14}\)

c: \(\dfrac{6\cdot9-2\cdot17}{63\cdot3-119}=\dfrac{54-34}{189-119}=\dfrac{20}{70}=\dfrac{2}{7}\)

a) \(\frac{1}{8}>0>\frac{-3}{8}=>\frac{1}{8}>\frac{-3}{8}\)

b) \(\frac{-3}{7}< 0< 2\frac{1}{2}=>\frac{-3}{7}< 2\frac{1}{2}\)

c) \(-3.9< 0< 0.1=>-3.9< 0.1\)

d) \(-2.3< 0< 3.2=>-2.3< 3.2\)

\(\dfrac{-11}{3^7\cdot7^3}=\dfrac{1}{3^7\cdot7^3}\cdot\left(-11\right)\)

\(\dfrac{-78}{3^7\cdot7^4}=\dfrac{-78}{3^7\cdot7^3\cdot7}=\dfrac{1}{3^7\cdot7^3}\cdot\dfrac{-78}{7}\)

mà \(-11>-\dfrac{78}{7}\)

nên \(\dfrac{-11}{3^7\cdot7^3}>\dfrac{-78}{3^7\cdot7^4}\)

Câu 1 : 

\(\dfrac{-25}{37}\&\dfrac{-20}{31}\)

Ta thấy \(\dfrac{-25}{37}< \dfrac{-20}{37}\)

mà \(\dfrac{-20}{37}< \dfrac{-20}{31}\)

\(\Rightarrow\dfrac{-25}{37}< \dfrac{-20}{31}\)

Câu 2 :

\(\dfrac{2}{3}\&\dfrac{5}{7}\)

\(\dfrac{2}{3}:\dfrac{5}{7}=\dfrac{2}{3}.\dfrac{7}{5}=\dfrac{14}{15}< 1\)

Ta thấy \(\dfrac{8}{13}:\dfrac{5}{7}=\dfrac{8}{13}.\dfrac{7}{5}=\dfrac{56}{65}< 1\)

a: \(x_1=x_2=x_3=x_4\)

\(\dfrac{-7}{24}\)