B

B

B

x + x + x +....+ x + 1+4+7+...+28= 155

có baonhiêu sô trong dãy là có bấy nhiêu số x

(28-1) : 3 + 1 = 10 số

10*x + (tổng ) = 155

tổng = (28+1) x 10 : 2 = 145

10*x + 145 = 155

x  =1

tick nhá

x + (1+4+7+10+.....+28)=155

x + (28+1) . 10 =155

x + 145 =155

suy ra x=155-145=10

1 installed

2 have visited

3 wil be watching

4 will be used

5 causes

6 is riding

7 has grown

8 is held

9 escaping

10 to have

VI

1 crowded

2 renewable 

3 inventor

4 Porvety

5 Recycleable

6 consume 

7 cultural

8 imaginative

Bài 4: 

\(8dm=0,8m\\ 15dm^2=0,15m^2\\ 20cm=0,2m\\ 600m^2=0,06ha\\ 3dm=0,3m\\ \dfrac{1}{100}ha=0,01ha\\ 800dm^2=8m^2\)

Bài 6: 

\(a,\dfrac{8}{10}=0,8\\ b,\dfrac{456}{1000}=0,456\\ c,\dfrac{15}{100}=0,15\\ d,\dfrac{3}{100}=0,03\\e,\dfrac{34}{1000}=0,034\\ g,\dfrac{6}{1000}=0,006\)

Bài 7: 

\(a,0,7=\dfrac{7}{10}\\ b,1,2=\dfrac{6}{5}\\ c,0,56=\dfrac{14}{25}\\ d,0,089=\dfrac{89}{1000}\\ e,0,235=\dfrac{47}{200}\\ g,0,009=\dfrac{9}{1000}\)

6

\(\Leftrightarrow5x=6\left(x-1\right)\Leftrightarrow5x=6x-6\Leftrightarrow x=6\)

ĐKXĐ:\(x\ne0\)

\(\dfrac{5}{6}=\dfrac{x-1}{x}\\ \Rightarrow5x=6\left(x-1\right)\\ \Rightarrow5x=6x-6\\ \Rightarrow6x-5x-6=0\\ \Rightarrow x-6=0\\ \Rightarrow x=6\)

3:

a: \(B=\dfrac{a^2-2a+1-a^2-a+3a+1}{\left(a+1\right)\left(a-1\right)}\cdot\dfrac{\left(a+1\right)\left(a-1\right)}{2a+1}\)

\(=\dfrac{2}{2a+1}\)

b: B=3/(a-1)

=>2/(2a+1)=3/a-1

=>6a+3=2a-2

=>4a=-5

=>a=-5/4

c: B>1

=>(2-2a-1)/(2a+1)>0

=>(-2a+1)/(2a+1)>0

=>(2a-1)/(2a+1)<0

=>-1/2<a<1/2

mà a nguyên

nên a=0

H và D ở đâu ra vậy em?