Chọn A. 49cm

@linhngocnguyen

If someone asks me about one historical figure that I like the most, it will definitely be President Ho Chi Minh. I am sure that President Ho is admired and loved not only by Vietnamese people but also residents in other countries around the world. He is a prominent leader and he led many resistances that defeated foreign invaders to bring peace and protect national sovereignty.

President Ho is well known for leading a simple life and spending all his life fighting for the happiness of Vietnamese people and the independence of the nation.

He was born into an impoverished but intellectual family in Nghe An province so he could understand the misery and poverty that were caused by war to Vietnamese people. Therefore, at a very young age of early twenty, he decided to go to some foreign countries to find a way to save the country. He went through a lot of ups and downs but with his decisiveness and patriotism, he came back to Vietnam with innovative ideas to improve the policies as well as eliminate invaders.

President Ho had achieved a lot in his life of doing politics; however, he never thought for himself only, he helped other people till the end of his life. Now there are many memorials of President Ho in different countries for people to honor one of the greatest men in the world’s history.

@linhngocnguyen

https://hoidap247.com/cau-hoi/4448549

DA-NI là j

là sao

ĐỀ BÀI KO ĐẦY ĐỦ

@kudoshin

tổng là:1,01699

ĐÂY LÀ DÃY SỐ CÁCH ĐỀU 3ĐƠN VỊ

@kudoshin

3

Đặt a1;S2=a1+a2;...;S

a1+a2+...+am+aSn=a1+a2+...+am+am+1+...+anSn=a1+a2+...+am+am+1+...+an

a⇒Sn−Sm=am+1+am+2+...+an⇒Sn−Sm=am+1+am+2+...+an tận cùng là 0

a⇒n−m=am+1+am+2+...+an⋮10⇒n−m=am+1+am+2+...+an⋮10

Vậy a1+a2+...+a10⋮10a1+a2+...+a10⋮10 (Đpcm)

Ta lập dãy số như sau:

Đặt B1 = a1

B2 = a1 + a2

B3­ = a1 + a2 + a3

….

B10 = a1 + a2 + a3 + … + a10

Nếu tồn tại Bi (i = 1, 2, 3, …, 10) nào đó chia hết cho 10 thì bài toán được chứng minh

Nếu không tồn tại Bi thì:

Ta đem Bi chia cho 10 sẽ được 10 số dư (các số dư từ 1 đến 9), Theo nguyên tắc Dirichlet, phải có ít nhất 2 số dư bằng nhau.

Các số Bm – Bn chia hết cho 10 (m > n)

Vậy thế nào cũng có một số hoặc tổng một số các số liên tiếp nhau trong dãy trên chia hết cho 10.

@kudoshin