Amin nào sau đây là amin bậc 2:

A.  C 6 H 5 N H 2  

B.  C H 3 − C H ( N H 2 ) − N H 2

C.  H 2 N − [ C H 2 ] 6 − N H 2

D.  C H 3 − N H −   C H 3

Kết quả của phép tính  4 x 9   là

A. 18

B. 27

C. 36

D. 45

Phương trình sin x = cos x  chỉ có các nghiệm là

A. x = π 4 + k π ,    k ∈ ℤ

B. x = π 4 + k 2 π ,    k ∈ ℤ

C. x = ± π 4 + k π ,    k ∈ ℤ

D. x = ± π 4 + k 2 π , k ∈ ℤ

Two students were asked about their hobbies and here is what they said.

Lien: Cooking is my favorite hobby. My grandmother taught me how to cook my first dish when I was 8. My family enjoyed it so much so that is when I started this hobby. Some people say cooking is a waste of time but I find this hobby very interesting and meaningful. I really love trying new food and cooking for my family. The feeling of making my family happy with my food is amazing. I often collect recipes from my mother and my grandmother. Sometimes I also get recipes from the internet. Then I write them in a notebook. I hope I will become a good chef and have my own cookery book in the future.

Cuong: I have an unusual hobby: carving eggshells. I started this hobby four years ago after getting a carved egg from my dad when he came back from Japan. It's amazing that something as fragile as an empty eggshell can be made into such a beautiful piece of art. I was so amazed that I learned how to carve them myself from the internet. I find carving eggshells a little difficult but so interesting and useful. The feeling of accomplishment when I finish a piece is absolutely awesome. This hobby also helps me be more patient and careful.

What does Cuong think about his hobby?

A. He finds it interesting.

B. He thinks it's difficult.

C. He finds it useful.

D. All are correct.

A. Yes, it is      

B. Yes, it did      

C. No, it wasn’t      

D. No, it hasn’t

Diện tích xung quanh của một hình nón có bán kính đáy bằng a và góc ở đỉnh bằng  60 °  là:

A.  2 π a 2

B.  2 π a 2 3 3

C.  π a 2 3

D.  π a 2

Trong không gian với hệ tọa độ Oxyz, cho mặt phẳng  P : y − 2 z + 1 = 0. Vectơ nào dưới đây là một vectơ pháp tuyến của (P)?

A.  n → = 1 ; − 2 ; 1 .

B.  n → = 1 ; − 2 ; 0 .

C.  n → = 0 ; 1 ; − 2 .

D.  n → = 0 ; 2 ; 4 .

Cho hàm số y = f(x) có bảng biến thiên sau:

Mệnh đề nào dưới đây đúng?

A. Hàm số có hai điểm cực tiểu

B. Hàm số có ba điểm cực trị

C. Hàm số có giá trị cực đại bằng 1

D. Hàm số có hai điểm cực trị