Tìm các cặp số nguyên dương x, y sao cho: 3x2y - 7y = 5x2 + 84
giúp mình với ngày mai phải nộp lại cho cô rùi! Hic...hic...
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LQ
17 tháng 12 2015
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
17 tháng 12 2015
x + (1+4+7+10+.....+28)=155
x + (28+1) . 10 =155
x + 145 =155
suy ra x=155-145=10
CT
2
10 tháng 6 2018
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 \(\frac{a}{b}>\frac{a+2007}{b+2007}\)
hu .... hu ..... hic ...... hic
DM
18 tháng 12 2016
An essential problem of the 21st century is world pollution. Currently the environment is so contaminated that urgent measures should be taken. A single individual cannot be blamed for the world pollution, however every person should take care of his or her habitat. In addition, it is vital that environmental issues are treated internationally.
Lately, many presentations, conferences and international summits are held to deal with waste treatment, recycling, and soil and water contamination. For sure joint efforts and consolidation can only help in the mutual war towards the ongoing environmental disaster. For instance, governments should offer support to companies and organizations, involved in manufacturing, industry or agriculture in order to find environment-friendly approaches. These could be special law regulations, recycling programs, helping courses in order to implement ISO certificates and many more.
However, the influence of individuals over environment should not be ignored. If we do not confess that our planet is our home, we will never be able to take adequately care of it. We have to contribute every day to the preservation of nature and environment. For example, always remember to save energy by switching off lamps, computers and everything that we do not use. Our next obligation is to separate waste and throw bulk only in the designated areas. Driving vehicles can also be environment friendly. For example, we have to avoid accelerating the engines too rapidly or using the air conditioning in the country, where it would be better to save energy and simply open the windows.
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.
18 tháng 12 2016
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
DA
7
15 tháng 1 2017
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)
15 tháng 1 2017
(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! :)
TM
7
1 tháng 8 2017
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
