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

Câu 6: D

Câu 7: C

6 D

7 C

8 C

9 D

10 A

11 C

Xét hiệu:

\(\frac{a}{b}-\frac{a+2007}{b+2007}=\frac{a.\left(b+2007\right)-b.\left(a+2007\right)}{b.\left(b+2007\right)}=\frac{ab+2007a-ab+2007b}{b.\left(b+2007\right)}=\frac{2007.\left(a-b\right)}{b.\left(b+2007\right)}\)

Xét 3 trường hợp:

TH1: a=b\(\Rightarrow\)a-b=0\(\Rightarrow\)\(\frac{2007.\left(a-b\right)}{b.\left(b+2007\right)}=\frac{2007.0}{b.\left(b+2007\right)}=0\)\(\Rightarrow\frac{a}{b}=\frac{a+2007}{b+2007}\)

TH2:  a<b\(\Rightarrow\)a-b<0\(\Rightarrow\)\(2007.\left(a-b\right)< 0\Rightarrow\frac{2007.\left(a-b\right)}{b.\left(b+2007\right)}< 0\)\(\Rightarrow\frac{a}{b}< \frac{a+2007}{b+2007}\)

TH3: a>b\(\Rightarrow\)a-b>0\(\Rightarrow\)\(2007.\left(a-b\right)>0\Rightarrow\frac{2007.\left(a-b\right)}{b.\left(b+2007\right)}>0\)\(\Rightarrow\frac{a}{b}>\frac{a+2007}{b+2007}\)

Vậy với a=b thì  \(\frac{a}{b}=\frac{a+2007}{b+2007}\)

            a<b thì \(\frac{a}{b}< \frac{a+2007}{b+2007}\)

           a>b thì  \(\frac{a}{b}>\frac{a+2007}{b+2007}\)

mấy bạn giúp mình với >.<

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To sum up, environmental problems should be handled by local and international authorities as well as individuals. Every single person should take care of the environment, moreover we have to bring up our children to be conscious citizens of a clean and preserved planet.

Life is increasingly enhanced by the technology works, scientific - increasingly advanced technology to serve human life. But along with this development is the future consequences that the people we have to suffer because of lack of awareness about environmental protection. Environment is what surrounds us, from the same identical green lawns, winding rivers forever or the mountains on the horizon, they all live in a world that is around us. But the fact is that, man is the murderer took away his own life by making the environment more severely polluted, especially in big cities and industrial centers. Every school day die due to the lack of a sense of protection of natural resources, deforestation, indiscriminate green lung puncture of the World or the litter, waste, toxic gases from factories now out of the canal, and the atmosphere is one thing we are alarming. Environmental pollution has become a hot issue of humanity. Summit to be held in Brazil in 1992 made the whole world call to work together to protect the earth - our planet, building the green environment - clean - beautiful. Vietnam we have enacted policies that protect natural resources and is willing to work with countries around the world to protect the environment. Students we must also be aware of environmental hygiene, actively participating in movement activities like "Green Sunday" total hygiene schools, neighborhoods, join afforestation, no discharge litter public places ... in short, environmental protection is to protect our lives

ta có 1 = 1 x 1 

ta xét 1 Th 

x + 1= 1 

=> x= 0 

và y - 2 = 1 

=> y = 3

Th âm tự xét 

1= (-1) x(-1)

(x + 1 ) ( y-2) = 1

=> x + 1 = 1 hoặc y - 2 =1

th1 : x + 1 =1

x = 1 -1 

x = 0

th2 : y - 2 = 1

    y = 1 + 2

    y = 3

Vậy : x = 0 ; y = 3

tk mk nha! :)

2

2 nha em

sửa lại:

dáp=> giáp

chôi=> trôi

?

Đề đâu???

GTNN:A=X²+2X+5

             =>A=5

       5=X²+2X+5

       =>X²+2X=0

      =>X=0

GTLN:M=4-/5x-2/-/3-y/

          M=4-/5.0-2/-/ 3-3/

           M=4-2-0=2

           N=5-2x-x²

          N =5-2*0-0²

         N=5

          Mik nghĩ vậy còn bạn sao thì ko bít