Nhớ nhấn nhé

Số số hạng của tổng A là 30-0+1=31 số
A=1 + 3 + 3² + 3³ +...+ 3³⁰=(1+3+3²+3³)+…+(3²⁴+3²⁵+3²⁶+3²⁷)+3²⁸+3²⁹+3³⁰
Đồng dư..0+..0+..0+…+…0+3²⁸+3²⁹+3³⁰=3²⁸+3²⁹+3³⁰(mod 10)
Ta có 3²=-1 mod(10) suy ra 3²⁸+3²⁹+3³⁰ đồng dư 1+3+9=13 mod 10 
Vậy A tận cùng là 3=> A không là số chính phương 

Có chút nhầm lẫn ở câu 8 : classes không phải recess .

Đặt câu hỏi cho các từ in nghiêng :

1 ..How often does she go to school ?..

- She goes to school six days a week.

2 …What do you learn in your computer science class?....

- We learn how to use a computer in computer science class.

3 …What is her favourite subject ?...

- Her favorite subject is English.

4 …How much is this book ?....

- This book is 30.000 dong.

5…What are they doing in the school yard ?.

- They are playing catch in the school yard.

6 …What do you usually do at recess ?...

- I usually talk with my friends at recess.

7 …Where is your father jogging ?....

- My father is jogging in the park.

8 …What time do the recess always begin ?.

- Classes always begin at seven o’clock.

Điền vào mỗi chỗ trống để tạo từ đúng :

1.recess

2.chat

3.pen pal

4.portable

Nó cầm dao và đấm vào ngực nó (vượn hay làm thế).

Điền giới từ thích hợp vào chỗ trống:

1._At_ school she learns lots of different things.

2.Mai is very interested _in_ computer.

3.She has Geography _on_ Monday and Thursday.

4._In_ her Geography class, she learns about different countries.

5. Ba is good _at_ fixing thing.

6.What do you usually do _at_ recess ?

7. What do you usually do _at_ recess ?

Điền giới từ thích hợp vào chỗ trống:

1._At_ school she learns lots of different things.

2.Mai is very interested _in_ computer.

3.She has Geography _on_ Monday and Thursday.

4._In_ hẻ Geography class, she learns about different countries.

5. Ba is good _at_ fixing thing.

6.What do you usually do _at_ recess ?