Tổng của cấp số nhân vô hạn :  1 2 ,   - 1 4 ,   . . . . ,   - 1 n + 1 2 n , . . . .   l à

A. 1

B. 1/3

C. -1/3

D. (-2)/3

1. Because some people say that this hobby is dificult and boring.

2. In an art galerry in US.

3. Some people find it's dificult and boring.

4. Yes, he does.

1.The teddy bear, the flower and the bird with flowers are on the eggshells.

2. I think it made of eggshells.

3. It’s carving eggshells.

Tìm các khoảng đồng biến của hàm số y = 4 x - 5 l n ( x 2 + 1 )

A.  - 2 ; 1 2

B.  - 1 2 ; 1 2

C.  - ∞ ; 1 2   v à   2 ; + ∞

D.  - ∞ ; - 1 2   v à   1 2 ; + ∞