186con.Đây là bài toán đố trong sách toán đấy!

Bấm đúng cho tớ nha!

chat?

Ex1

1) Since I joined the company, I have been to over twenty countries

2) They have been friends for five months

3) He has watched TV for three hours

4) I have wanted that book for months

5) I haven't seen you since Chrismast

6) I haven't eaten any meat for over a year

Ex2

1) Susan come quickly! The milk is boiling over and making an awful mess of the kitchen.

*Câu 4 Ex1 hình như đề bạn nhập bị thiếu thì phải? Mình chỉ thắc mắc vậy thôi! ^^

kỉ lục                      

Yu need to be patient to follow eggshell carving because it may takes two weeks to complete on shell.

Alice is late for school because she's very slow.

\(A=n\left(n^2+1\right)\left(n^2+4\right)\)

+ n  ≡ 0 (mod 5)
=> n⋮5 => A⋮5

+ n  ≡ 1 (mod 5)
=> n²  ≡ 1 (mod 5)
=> n² + 4⋮5
=> A⋮5

+ n ≡ 2 (mod 5)
 => n² ≡ 4 (mod 5)
=> n² + 1⋮5
=> A⋮5

+ n ≡ 3 (mod 5)
 => n² ≡ 3²  ≡ 4 (mod 5)
=>n² + 1⋮5
=> A⋮5

+ n ≡ 4 (mod 5)
=>n² ≡ 4² ≡ 1 (mod 5)
=> n² +4⋮5
=> A⋮5

Vậy A luôn chia hết cho 5.

Bn thi OSE ak?