2:

a: BC=căn 15^2+20^2=25cm

AH=15*20/25=12cm

góc ADH=góc AEH=góc DAE=90 độ

=>ADHE là hình chữ nhật

=>DE=AH=12cm

b: ΔAHB vuông tại H có HD vuông góc AB

nên AD*AB=AH^2

ΔAHC vuông tại H có HE vuông góc AC

nên AE*AC=AH^2

=>AD*AB=AE*AC

c: góc IAC+góc AED

=góc ICA+góc AHD

=góc ACB+góc ABC=90 độ

=>AI vuông góc ED

4:

a: góc BDH=góc BEH=góc DBE=90 độ

=>BDHE là hình chữ nhật

b: BDHE là hình chữ nhật

=>góc BED=góc BHD=góc A

Xét ΔBED và ΔBAC có 

góc BED=góc A

góc EBD chung

=>ΔBED đồng dạng với ΔBAC
=>BE/BA=BD/BC

=>BE*BC=BA*BD

c: góc MBC+góc BED

=góc C+góc BHD

=góc C+góc A=90 độ

=>BM vuông góc ED

Hello, this year I am twelve years old. I live with my family in a small lovely house on the outskirts of the city. Every day, my mother wakes me up at five thirty. The atmosphere is fresh then. At this time, some other families also wake up, they go to the market, do exercises, prepare the energy for a new day. I always water vegetables and feed chickens in the garden with my father. Then I back to my room, do personal hygiene and get dress, prepare books to go to school. When I get downstairs, my mother is busy with preparing breakfast for the whole family in the kitchen. After eating, my father takes me to school by motorbike because my school is quite far away from my house. At school, I have many friends, they are all very cute and docile. At the breaks, we often play some folk games such as horse jumping, blindfolded goats, box office, ... In addition, I also paripate in some clubs such as book, piano and english club. After school, I and some of my friends often clean the class and study in the group. At night, I help my mother with cooking and then family members gather in the living room to watch the favorite TV channels, share the story of the day. Before going to bed, my father always brings me a glass of milk and check my study. Every day is a great and invaluable gift, the work even seems small but brings me joy and happiness.

In the morning, I wake up at 9 o'clock. By this time, the sky had long since dawned. I look in the mirror and smile, it motivates me for a new day. Then, I brush my teeth and wash my face. After that, I have breakfast. Sometimes, because I get up too late, I don't eat breakfast. At 10 a.m, I do my homework. When I finish my homework, it is 11.30, so I have a lunch. I take a rest at 12.15. I think that. In the afternoon, I do housework with mom and dad. Then we have a dinner. After that, we watch TV. When it is 10 o'clock, we go to bed and sleep.

@Cỏ

#Forever

Hãy gọi thế giới của tôi là cái ghế vì độ chất của nó không phải bàn.

vì 4:3=2x2=4 hihi 

4:3=2

4:3 là  tứ chia tam là tám chia tư

vậy 8:4=2

cc

16 teach

17 causes

18 build

19 married

20 fewer

may có tao nha

1A house had been built for her parents in Da Lat by her

2.Something must be done for these poor man

3. Mistakes haven't been made

4.Jane was promised a prize by the teacher if she worked well

5. I wasn't spoken like that before

42 lived here for 10 years

43 you work hard, you will be sacked

44 owner of this house

45 different from mine

X

1 It is famous for its long teaching history

2 in 1070

3  No, they didn't

4 It closed in 1802

5 Yes, they can

42. I have lived here for ten years.

43. Unless you work hard, you will be sacked.

44. Mr. Hung is the owner of this house.

45. Her bag is different from mine.

46. It is famous for its long teaching history.

47. In 1070

48. No, they didn't

49. In 1082

50. Yes, they can

Gọi vận tốc thực là x

Độ dài quãng đường AB là 4(x+2)

Theo đề, ta có phươg trình:

4(x+2)=5(x-2)

=>5x-10=4x+8

=>x=18

Vậy: Độ dài quãng đường là 80km