Cho phương trình a x 2  + bx + c = 0 (a  ≠ 0) có biệt thức b = 2b'; △ ' = b ' 2  - ac. Nếu  △ ' = 0 thì:

A. Phương trình có hai nghiệm phân biệt

C. Phương trình có nghiệm kép  x 1  =  x 2  =  - b ' a

D. Phương trình có nghiệm kép  x 1  =  x 2  =  - b ' 2 a

Read the following passage, and decide if the statements are T or F.

Alexander Graham Bell is widely known as inventor of the first telephone. He was born on March 3^rd, 1847 in Edinburgh, Scotland. When he was 23, Bell emigrated to Canada with his parents and the next year moved to the United States to teach deaf-mute children. With his colleague Thomas Watson, Bell worked very hard on the experimentation to invent devices such as the harmonic telegraph(used to send multiple messages over a single wire) andphonautograph (used to draw the shape of the sound waves). The first telephone communication was said to have happened between Bell and Watson in 1876 while Bell was at one end of the line, and Watson worked on the telephone in other room. The first transmitted words were, ‘Mr Watson, come here. I want to see you’.

Question: He worked with the deaf when he moved to the USA.

A. True

B. False

Giá trị của biểu thức (-63).(1-299) - 299.63 là:

A. – 63

B. 63

C. – 53

D. 53