1. Peter and his brother has learnt English for three years.

2. Mr.Green has played chess since eight o'clock.

3. It hasn't rained since last week.

4. We haven't seen our new teacher yet.

5. I have studied very hard for this examination.

6. My uncle has worked in this factory for ten years.

7. She saw this film before

8. The weather has been quite good since Chirtmas.

9. I have had this bike since I was a teenager, and I still use it.

10. He is playing for the football club for several years, but it's tim to leave it now.

Nếu cạnh của hình lập phương tăng lên 3 lần thì thể tích của hình lập phương cũng tăng lên 3 lần.

A = 6/19 . -7/11 + 6/19 . -4/11 + -13/19

A = 6/19 . [-7/11 + (-4/11)] + (-13/19)

A = 6/19 . -11/11 + (-13/19)

A = 6/19 . (-1) + (-13/19)

A = -6/19 + (-13/19)

A = -19/19

A = -1

Vậy A = -1

Đầu bài của bạn thiếu rồi.

Thân mọng nước để dự trữ nước cho cây.

Lá biến thành gai để bảo vệ cây.

a) 17/23 . 8/16 . 23/17. (-80) . 3/4

= (17/23 . 23/17) . (8/16 . 3/4) . (-80)

= 1 . 3/8 . (-80)

= 3/8 . (-80)

= -30

b) 5/11 . 18/29 - 5/11 . 8/29 + 5/11 . 19/29

= 5/11 . (18/29 - 8/29 + 19/29)

= 5/11 . 1

= 5/11

c)(13/23 + 1313/2323 - 131313/232323).(1/3+1/4 -7/12)

= (13/23 + 1313/2323 - 131313/232323).0

= 0

d) 1²/2x2 . 2²/2x3 . 3²/3x4 . 4²/4x5 . 5²/5x6 . 6²/6x7 . 7²/7x8 . 8²/8x9 . 9²/9x10

= 1/2 . 2/3 . 3/4 . 4/5 . 5/6 . 6/7 . 7/8 . 8/9 .9/10

= 1/10

Khó nhìn quá. Bạn thông cảm nhé!

A = 2/7 + 1/9 +1/7 + 5/9 + 8/14

A = (2/7 + 1/7) + (1/9 + 5/9) + 4/7

A = 3/7 + 6/9 + 4/7

A = 3/7 + 2/3 + 4/7

A = (3/7 + 4/7) + 2/3

A = 7/7 + 2/3

A = 1 + 2/3

A = 5/3

Vậy A = 5/3