You should not register the questions of the linh tinh as such as this program

A=1+2+3+...+49+50

We have 2A=1+2+3+...+49+50+1+2+3+...+49+50

                   =(1+50)+(2+49)+...+(50+1)

                   =51+51+...+51

   =>A=51.50:2=1275

We have:

k(k+1)(k+2)-(k-1)k(k+1)=k(k+1)(k+2-k+1)=3k(k+1)

=>k(k+1)=\(\dfrac{k\left(k+1\right)\left(k+2\right)}{3}\)-\(\dfrac{\left(k-1\right)k\left(k+1\right)}{3}\)

Ta post S

S = 1+3(1+3^2+...+3^49)=1+3(S-3^50)

=>S=1+3S-3^51

=>2S=3^51-1=>S=\(\dfrac{3^{51-1}}{2}\)

Ta viết S dưới dạng

There are 31 days in the month

Countries very much
 

Afghanistan

Albania

Algeria

Andorra

Angola

Antigua & Barbuda

Armenia

Argentina

Australia

Austria

Azerbaijan

The Bahamas

Bahrain

Bangladesh

Barbados

Belgium

Belarus

Bhutan

Bolivia

Benin

Belize

Botswana

Brazil

Brunei

Bulgaria

Cambodia

Cameroon

Canada

Central African Republic

Chile

Chad

China

Colombia

Comoros

Costa Rica

Egypt

Ecuador

France

Finland

Germany

Greece

India

Italy

Japan

Korea, South

Netherlands

Norway

Portugal

Russia

Spain

Taiwan

Thailand

United States

Vietnam

Turkmenistan

   \(\dfrac{1}{2}\)+\(\dfrac{2}{3}\)+\(\dfrac{3}{4}\)+\(\dfrac{1}{3}\)

=\(\dfrac{7}{6}\)+\(\dfrac{3}{4}\)+\(\dfrac{1}{3}\)

=\(\dfrac{23}{12}\)+\(\dfrac{1}{3}\)

=\(\dfrac{9}{4}\)

 We have:

4=2^2

6=2.3

8=2^3

BCNN(4,6,8)=2^3.3=8.3=24

We have:

10=2.5

20=2^2.5

30=2.3.5

=>ƯCLN (10,20,30)=2.5=10

X-10+2=20+10

X-10+2=30

X-10=30-2

X-10=28

X=28+10

X=38

A = {0; 1; 2; ...; 49}

or 

B= {11,12,...,99 

{x∈N|10<x<100}⇔B={x∈N|10<x<100}

or 

A,46+17+54

=(46+54)+17

=100+17

=117

B,4.35.25

=(4.25).35

=100.35

=3500

Answer:56 students

sao mấy bạn có thể nói mk như vậy

Sao mk thấy vậy trả lời sao bạn kêu mk tự ra câu hỏi tự trả lời

75+20+45+55+80

=(20+80)+(45+55)+75

=100+100+75

=100x2+75

=200+75

=275

75+34+43+25+66

=(75+25)+(34+66)+43

=100+100+43

=100x2+43

=200+43

=243

I math

75+34+43+25+66+57

=(75+25)+(34+66)+(43+57)

=100+100+100

=100x3

=300