Cho hình thang cân ABCD (AB//CD) có DB vuông góc với BC và DB là tia phân giác của góc ADC. a, Tính các góc của hình thang b, Biết BC = 6cm. Tính chu vi hình thang (giúp mình với ạ)
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- "I'll come and see you as soon as I can," he/she said.
- My teacher said, "You should practice speaking English everyday."
- She told her son, "Go straight upstairs and get into bed."
- The lifeguard said, "Don't swim out too far, boys."
- He asked Huong, "Could you give me a hand, please?"
- The traffic police said, "Show me your driving license, please."
- Nien asked Hoa, "Do you have many new friends?"
- They told us, "You must go now."
- I asked Nam, "Are you free tonight?"
- The visitors asked, "Can we take photos?"
- She asked, "Do you know the way to the station?"
- "Will I finish my exercise at home?" he/she asked.
- She asked Minh, "Can you speak Chinese?"
- The girl asked, "How old is your grandparent?"
- They asked, "Who are you going with tomorrow?"
- I asked Tam, "Do you want to visit the Great Wall in China?"
- I asked the tourist, "Are you from Canada?"
- I told Lan, "Send me a postcard when you arrive in Paris."
- Thu asked Hoa, "Why is she crying?"
- Mrs. Ly asked, "When do your children go swimming?"
- "I'll come and see you as soon as I can," he/she said.
- My teacher said, "You should practice speaking English everyday."
- She told her son, "Go straight upstairs and get into bed."
- The lifeguard said, "Don't swim out too far, boys."
- He asked Huong, "Could you give me a hand, please?"
- The traffic police said, "Show me your driving license, please."
- Nien asked Hoa, "Do you have many new friends?"
- They told us, "You must go now."
- I asked Nam, "Are you free tonight?"
- The visitors asked, "Can we take photos?"
- She asked, "Do you know the way to the station?"
- "Will I finish my exercise at home?" he/she asked.
- She asked Minh, "Can you speak Chinese?"
- The girl asked, "How old is your grandparent?"
- They asked, "Who are you going with tomorrow?"
- I asked Tam, "Do you want to visit the Great Wall in China?"
- I asked the tourist, "Are you from Canada?"
- I told Lan, "Send me a postcard when you arrive in Paris."
- Thu asked Hoa, "Why is she crying?"
- Mrs. Ly asked, "When do your children go swimming?"
nếu bạn sử dụng máy tính bạn có thể làm như sau:
1. Đưa con trỏ chuột vào 1 tên bất kì.
2. Nó sẽ hiện lên thông tin về nơi học, điểm xs, điểm hỏi đáp,... Ta sẽ thấy 1 khung chữ nhật màu xanh dương có hình người và dấu cộng kế bên.
3. Nhấn vào nút đc chỉ dẫn ở bước 2, nó sẽ hiện lên chữ " hủy lời mời" là ta đã kết bạn thành công. Chỉ cần chờ ng đó kết bạn nữa là xong
Không, câu chuyển đổi của bạn không chính xác. Câu "Because Hoa was rich, she could buy that house" có nghĩa là Hoa có thể mua căn nhà đó vì cô ấy giàu có. Để chuyển đổi câu này, bạn có thể sử dụng cấu trúc "Because of + danh từ" như sau: "Because of her wealth, Hoa could buy that house" (Vì giàu có, Hoa có thể mua căn nhà đó).
sai rồi, phải là:
Because of her wealth, Hoa could buy that house.
như thế này mới đúng này
Ta có
\(\dfrac{x}{a}=\dfrac{y}{b}=\dfrac{z}{c}\Rightarrow\dfrac{x^2}{a^2}=\dfrac{y^2}{b^2}=\dfrac{z^2}{c^2}=\dfrac{x^2+y^2+z^2}{a^2+b^2+c^2}=x^2+y^2+z^2\) (1)
Ta có
\(\dfrac{x}{a}=\dfrac{y}{b}=\dfrac{z}{c}=\dfrac{x+y+z}{a+b+c}=x+y+z\)
\(\Rightarrow\dfrac{x^2}{a^2}=\dfrac{y^2}{b^2}=\dfrac{z^2}{c^2}=\left(x+y+z\right)^2=x^2+y^2+z^2+2\left(xy+yz+zx\right)\) (2)
Từ (1) và (2)
\(x^2+y^2+z^2=x^2+y^2+z^2+2\left(xy+yz+zx\right)\)
\(\Rightarrow xy+yz+zx=0\)
1. c. when she left the party.
2. b. he had bought the book yesterday.
3. c. didn’t
4. b. how long I had been
5. c. She asked, “ What time is it?”
6. c. He asked me whose motorbike I had borrowed last night.
7. c. She asked if I liked a cup of coffee.
8. b. He asked me if I had closed the windows when I left.
9. b. She wanted to know what I was going to do this weekend.
10. b. had just gone
11. b. whose book was on his desk
12. d. Please sit next to Mary.
13. c. asked us who had written the letter.
14. c. did she enjoy her music class.
15. c. we always try to please me.
16. d. She told me to be careful because the paint was wet.
17. d. Jenny asked if she could make an appointment to see the doctor.
18. c. He asked me if they had told me when they left school.
19. c. She asked, “How old was Jimmy?”
20. a. He asked me when my sister arrived.
21. c. if he was the man who had come here the day before
22. c. shut the door, don’t lock it.
23. c. he had just finished typing
24. b. if I would come
25. a. What your name is
26. d. she puts
27. d. it is
28. c. if
29. a. liked
30. c. This
31. c. might
32. b. there is
33. a. those
1) \(...=20x^3-10x^2+5x-20x^3+10x^2+4x\)
\(=9x=9.\left(-15\right)=-135\left(x=-15\right)\)
a, A = 1002 - 992 + 982 - 972 +...+ 22 - 12
A = (1002 - 992) + (982 - 972) +...+ (22 - 1)2
A = (100 - 99)(100+99) + (98-97)(98+97)+..+(2-1)(2+1)
A = 1.199 + 1.195 + 1.191 +...+1.3
A = 3 + ...+191+ 195 + 199
Dãy số trên là dãy số cách đều với khoảng cách là: 199 -195=4
Dãy số trên có số hạng là: (199 - 3): 4 + 1 = 50 (số )
A = (199 +3) \(\times\) 50 : 2 = 5050

a) Gọi \(\widehat{ADB}=\widehat{D_1;}\widehat{CDB}=\widehat{D_2}\)
Xét Δ vuông BDC ta có :
\(\)\(\widehat{D_2}+\widehat{C}=90^o\)
mà \(\widehat{D_2}=\dfrac{\widehat{D}}{2}\) (DB là phân giác \(\widehat{ADC}\))
\(\widehat{C}=\widehat{D}\) (ABCD là hình thang cân)
\(\Rightarrow\dfrac{\widehat{D}}{2}+\widehat{D}=90^o\)
\(\Rightarrow\dfrac{\widehat{3D}}{2}=90^o\Rightarrow\widehat{D}=60^o\Rightarrow\widehat{C}=\widehat{D}=60^o\)
Ta lại có : \(\widehat{A}+\widehat{B}+\widehat{C}+\widehat{D}=360^o\)
mà \(\left\{{}\begin{matrix}\widehat{A}=\widehat{B}\\\widehat{C}=\widehat{D}\end{matrix}\right.\) (ABCD là hình thang cân)
\(\Rightarrow2\widehat{A}+2\widehat{C}=360^o\Rightarrow\widehat{A}=\widehat{B}=\dfrac{360^o-2\widehat{C}}{2}\)
\(\Rightarrow\widehat{A}=\widehat{B}=\dfrac{360^o-2.60^o}{2}=120^o\)
b) \(BC=AD=6\left(cm\right)\) (ABCD là hình thang cân)
Xét Δ vuông BDC ta có :
\(Cos60^o=\dfrac{BC}{DC}=\dfrac{1}{2}\)
\(\Rightarrow DC=2BC=2.6=12\left(cm\right)\)
\(DC^2=BD^2+BC^2\left(Pitago\right)\)
\(\Rightarrow BD^2=DC^2-BC^2=12^2-6^2=144-36=108=3.36\)
\(\Rightarrow BD=6\sqrt[]{3}\left(cm\right)\)
Kẻ đường cao AH và BE vuông góc DC tại H và E
Ta có : \(BE.CD=BD.BC\Rightarrow BE=\dfrac{CD}{BD.BC}=\dfrac{12}{6.6\sqrt[]{3}}=\dfrac{1}{3\sqrt[]{3}}\left(cm\right)\)
Xét Δ BEC ta có :
\(BC^2=BE^2+EC^2\Rightarrow EC^2=BC^2-BE^2=36-\dfrac{1}{27}\)
\(\Rightarrow EC^2=\dfrac{971}{27}\Rightarrow EC=\dfrac{1}{3}.\sqrt[]{\dfrac{971}{3}}\left(cm\right)\)
ABHE là hình chữ nhật (AB \(//\) HE;AH \(//\) BE vì cùng vuông với CD; Góc H=90o )
\(\Rightarrow AB=HE=CD-2EC=12-\dfrac{2}{3}.\sqrt[]{\dfrac{971}{3}}\left(cm\right)\) (tính chất hình thang cân)
Chu vi hình thang cân ABCD :
\(2BC+DC+AB=2.6+12+12-\dfrac{1}{3}.\sqrt[]{\dfrac{971}{3}}=36-\dfrac{1}{3}.\sqrt[]{\dfrac{971}{3}}\left(cm\right)\)