a) Xét ΔDEI và ΔDFI c

DE = DF (ΔDEF cân)

DI là cạnh chung.

IE = IF (DI là trung tuyến)

➩ ΔDEI = ΔDFI (c.c.c)

b) Vì  ∆DEI  = ∆DFI => \(\widehat{DIE}\) \(= \widehat{DIF}\)

mà \(\widehat{DIE}\)+\(\widehat{DIF}\)=180⁰( kề bù)

nên \(\widehat{DIE}\)\(= \widehat{DIF}\)=90⁰

c) I là trung điểm của EF nên IE = IF = 5cm.

ΔDIE vuông tại I

➩ DE²=DI²+EI² (định lí Pitago)

➩ DI²=13²–5²=144

➩DI=12.

 Choose the right answer to complete the sentence:

1. Could you help me .............. the cooking?

A. with    B. by    C. for      

2. He teaches me ........... tennis.

A. to play      B.play        C. playing       

3. I had to ................ from the bank for my car.

A. send            B.borrow               C. take

5.B 

Choose the right answer to complete the sentence:

1. He has plenty of homework ............. tonight .

A. to do      B.do     C. doing         D. doing

2. Nam often spends an hour a day ............. video games.

A. to play      B.playing        C. to do        D. doing

3. The students have a ................. break between two perods.

A. five-minutes    B. five minute  C. five-minute

4. The noise ............. me awake at night.

A. takes     B. keeps        C. gives

5. The baby began ..............

A. cry       B. to cry           C. cries

 Choose the right answer to complete the sentence:

1. Do you know that video games may be ............?

A. addicted      B. addiction      C. addictive          D. added

2. ....................... people play video games.

A. Millions      B. Millions of         C. Million of        D. Million

3. Some play them at home,...... play them in the arcades. 

A. others         B. other          C. another          D. the other 

4. Children shouldn't spend much time on these games........... a long time.

A. in          B. on          C. for            D. during 

5. They can become ...................

A. dizzily          B. dizzy           C. dizzilily         D. dizziness

Our country is developing more and more thanks to the prosperity of the economy in recent years. But besides that, there are still some shortcomings including traffic problem. Traffic problem is becoming increasingly inadequate and becoming a red alarm problem in Vietnam. And compliance with traffic safety laws becomes extremely important.
Traffic accident situation is progressing more and more complicated and at an alarming rate. Every day people die and are injured in traffic accidents. People cannot help shuddering by the numbers of human damage caused by traffic accidents: every day about 35 people die, each year tens of thousands of people die in traffic accidents. This is a talking number.
Traffic accidents leave mourning for many families, leaving children with no parents, broken families. Besides, it also causes so much harm to the family and society. There are many foreign tourists coming to Vietnam who are just afraid of the mess of Vietnamese traffic. They are afraid to walk across the road when traffic is rushing, there is no sidewalk for pedestrians.
Because of the unsafe traffic in Vietnam affects the attraction of foreign investment in our country due to the chaos and insecurity of the country's traffic. There are many causes of traffic unsafety in our country. First, our people's awareness is low, our people's attitude and traffic awareness are too poor. When participating in traffic, everyone wants to go first, no one will yield to anyone, leading to traffic unsafety. Because this phenomenon leads to the situation of not giving up at intersections, intersections ... causing traffic jams for hours, the phenomenon of speeding, overtaking, swinging and deflecting is the leading cause. to traffic accident.
One of the other important causes of traffic accidents is the poor quality of bridges and roads: old bridges, weak bridges, poor quality; However, the traffic volume of vehicles and people is too much, leading to a situation of continuous upgrading and repairing affecting the quality of traffic. Another cause of this situation is their self-interest, they are willing to use vehicles that are out of date, speeding, carrying passengers over the prescribed number of people, leading to an accident. .
To minimize traffic accident, we need to take certain measures. First of all, it is necessary to propagate to the people about the consequences caused by traffic accidents, propagate that each citizen should comply with traffic safety laws. In addition, there should be appropriate penalties for people who knowingly violate traffic safety laws.
The State needs strategic solutions to improve the quality of roads to reduce traffic accidents. we need to care. The Party and State need to have more appropriate policies for a better civilized society.
Compliance with the current traffic safety law is a matter of great concern to the Party and the State because it has a great impact on the cause of building a rich and powerful country. Each citizen must voluntarily strictly abide by the traffic laws to contribute to making the society civilized and modern.

Đưa lần lượt thanh nhựa sẫm màu và thanh thuỷ tinh lại gần ống nhôm:

- Nếu cả 2 trường hợp này ống nhôm đều bị hút thì ống nhôm chưa nhiễm điện.

- Nếu một trong 2 trường hợp ống nhôm bị đẩy thì chứng tỏ ống nhôm đã nhiễm điện cùng dấu vơí điện tích của vật đã đẩy nó.

Trong sách hết đó ạ.