cho a, b , c lập thành 1 cấp số cộng 

 1, a²   + 8bc = ( 2b +c ) ²

xác định U1 và d biết 

a , \(\left\{{}\begin{matrix}u_2+u_4+u_6+...............+u_{2n}=126\\u_2+u_{2n}=42\end{matrix}\right.\)

b , \(\left\{{}\begin{matrix}u^3_1+u^3_{15}=30209\\S_{15}=583\end{matrix}\right.\)

Chứng minh , kiểm tra 1 dãy số có là cấp số cộng hay không ? xác định U1 , d

a , \(\left\{{}\begin{matrix}u_1\\u_n+1=u_n-n\end{matrix}\right.\)

b , \(\left\{{}\begin{matrix}u_1=a\\u_n+1=5\end{matrix}\right.\)       tìm a để d số là cấp số cộng 

bài 1 : cho 1 điện tích điểm 9.10^-12 C . Tính cường độ điện trường tại điểm M cách q là 1 khoảng 20 cm . Nếu nhúng điện môi thif cường độ điện trường là bao nhiêu ( v= 20 )

Giải phương trình lượng giác

1 , \(\sin2x-2\sqrt{2}\left(sinx+cosx\right)=5\)

2 , \(1+sin\frac{x}{2}sinx-cos\frac{x}{2}sin^2x=2cos^2\left(\frac{\pi}{4}-\frac{x}{2}\right)\)

Question 2

: 1.This month always has fewer days than other months. Which month is it?

2.What month is five months after September?

3.Which months have 30 days in year?

4.What date is 30 days after 20th Oct?

5. What day was it which Vietnam got independence?

6. When was Vo Nguyen Giap General born?

7. What day is your idol birthday ?

8. What is the date next Sunday?

9. When was Uncle Ho died?

10. In the future, there are a day which get date, month, year include six the two. What day is it ?

Question 6: When was Vo Nguyen Giap General born ?

Question 2

: 1.This month always has fewer days than other months. Which month is it?

2.What month is five months after September?

3.Which months have 30 days in year?

4.What date is 30 days after 20th Oct?

5. What day was it which Vietnam got independence?

6. Where was Vo Nguyen Giap General born?

7. What day is your birthday idol?

8. What is the date next Sunday?

9. When was Uncle Ho died?

10. In the future, there are a day which get date, month, year include six the two. What day is it ?

Ex 1 : Write the correct preposition of time.

1. Mary wore a witch costume ______ Halloween.

2. I have English classes ______ Tuesdays.

3. My dad comes home ______ lunchtime.

4. The children like to go to the park ______ the morning.

5. Henry's birthday is ______ November.

6. Lots of people go shopping ______ Christmastime.

7. Justin Bieber was born ______ March 1, 1994.

8. Leaves turn red, gold and brown ______ Autumn.

9. My friends like to go the the movies ______ Saturdays.

10.The pilgrims arrived in America ______ 1620.

11. My sister likes to watch TV ______ the evening.

12. Mum always reads stories ______ bedtime.

13. I like to watch the parade ______ Independence Day.

14. Hippies protested against the war ______ the 1960s.

15. We finished the marathon ______ the same time

viết 1 đoạn văn 200 chữ nêu suy nghĩ của anh chị về vai trò lí tưởng của tuổi trẻ sau khi đọc đoạn thơ Núi Đồi - Vũ Cao