Khẳng định nào sau đây đúng nhất?

A. Hàm số  y = x - 3  đồng biến trên  3 ; + ∞

B. Hàm số C nghịch biến trên  - ∞ ; 3

C. Hàm số  y = x - 3  đồng biến trên  - ∞ ; 3

D. Cả hai khẳng định A và B đều đúng

Read the passage carefully and choose the correct answer.

Different relationships  affect teenagers in various ways. Friends impact teenagers almost the same amount as their parents. Teenagers go to their friends for help or to ask questions that they could not ask their parents about. Most of the time their friends give them good advice. In most cases they tell their friends how to dress and act when being around certain people. Love relationships just make it even harder for a teenager to get a good education. Some start to fail in school because they are hanging out with their boyfriend or girlfriend instead of doing their work. Parents have a big influence on teenagers because their children look up to them and the majority of them grow up to act and do things just like their parents did with them. Children who have experienced a family break-up may have lower achievements than children brought up in an intact family. As previously stated, teenagers are affected by many relationships which involve their friends, family, and their love relationships. The relationships affect them so much that most teenagers change their ideas about how they should live their lives in a different way and to change their future goals. They should be influenced to help themselves or to help others.

Question: All of the following statements about parents’ influence on teenagers are true EXCEPT that______.

A. achievements of teenagers from a family break-up are always low

B. parents have a great impact on teenagers

C. most teenagers grow up to act and do things just like their parents

D. a family break-up may have a negative effect on teenagers

Có bao nhiêu cặp số thực (x; y) sao cho (x+1)y, xy và (x-1)y là số đo ba góc một tam giác (tính theo rad) và  sin 2 x + 1 y = sin 2 x y + sin 2 x - 1 y

A. 4

B. 1

C. 3

D. 2