a) ta có : ΔABC cân tại A
H là trung điểm cạnh AB
K là trung điểm cạnh AC
=> AH=HB và AK=KC
=> AH=HB=AK=KC
định lí 3 đường cao tam giác cân
=> HD=KD
xét Δ HDB và Δ KDC có :
H=K=90*
HB=KC (cmt)
HD=KD (cmt)
=> Δ HDB = Δ KDC (c.g.c)
=> DB=DC (2 cạnh tương ứng)
b) kẻ tia AM ⊥ BC
ta có : $B$1=$C$1(cmt)
=> $B$2=$C$2
=> ΔBDC cân tại D
=> DM ⊥ BC
mà AM⊥BC
=> D ∈ AM
=> A,D,M thẳng hàng
Giải thích các bước giải:
Gọi CM, BN là 2 đoạn trung trực.
D là trực tâm tam giác ABC.
AM là trung tuyến }
} AM là trực tuyến
ABC cân tại A }
⇒ A,D,M thẳng hàng
Xét Δ BMD và Δ DMC
DM chung
MB = MC } ∡Δ=Δ
} ∡ DB= DC
D MB = DMC = 90 độ
Một vật AB cao 2cm.Đặt trc gương phẳng cách gương 1,5 cm như hình vẽ: a)Hãy xác định tính chất và vị trí của ảnh A'B' b)Vẽ ảnh A'B' qua gương c)Khi dịch chuyển vật ra xa gương thêm 2cm thì ảnh A'B' dịch chuyển như thế nào?
Gúp với : tính nhẩm bằng cách áp dụng tính chất kết hợp của phép nhân: A)21×4 B)44×25 C)125×56 D)19×8
Make up sentences using the words and phrases given. 1. when/ I/ ten/ begin/ play football. ................................................................................................. 2. in/ future/ my father/ go abroad. ................................................................................................. 3. read/ books/ free time/ is/ favourite/ hobby. ................................................................................................. 4. I/ think/ skate/ more/ interesting/ mountain - climbing. ................................................................................................. 5. I /not/ know/ why/ my mother/ cook. ................................................................................................. 6. He/ collect/ books/ whenever/ have/ money. ................................................................................................. 7. How many/ paintings/ she/ paint? ................................................................................................ 8. I/ love/ flowers/ so/ I/ plant/ around/ house. ................................................................................................
Trường hợp cạnh - cạnh - cạnh Bài 1. Cho góc nhọn xOy.Trên Ox,Oy tương ứng lấy A và B khác O sao cho OA=OB.Vẽ hai đường tròn tâm A và B có cùng bán kính sao cho chúng cắt nhau tại M và N nằm trong góc xOy.Chứng minh rằng: a)Ba điểm O,M,N thẳng hàng. b)Chứng minh MN là tia phân giác của góc AMB. Bài 2.Cho tam giác ABC có AB=AC.Gọi H là trung điểm cạnh BC. a)Chứng minh AH là tia phân giác góc BAC và AH vuông góc BC. b)Trên tia đối tia HA lấy K sao cho HK=HA.Chứng minh CK//AB. Bài 3.Cho tam giác ABC có đường cao AH.Trên nửa mặt phẳng bờ AC không chứa B vẽ tam giác ACD sao cho AD=BC,CD=AB.Chứng minh rằng:AB//CD và AH vuông góc AD.
The painter Craigie Aitchitson was born in Scotland. He came to London intending to study law, but went to art school instead. There he found the traditional drawing classes difficult, but still kept on painting. In his late twenties, he was given money by the Italian government to study art, and became interested in early Italian artists, which shows in some of his work. He loved the greens and browns of the Italian fields and the clear light there, and wanted to put this light into his paintings. This led him to paint colors thinly one on top of another from light to dark, but he insists he’s never sure what the results will be. He says, “It’s a secret – because I don’t know myself. I don’t start by painting yellow, knowing I’m going to put anything on top.” Like most talented people, Atchison makes it sound easy. “Anyone can do the colors – you can buy them. I simply notice what you put the colors next to.” Unlike some artists, he never does drawings before he starts a painting, as he feels that if he did, he might get bored and not do the paintings afterwards. Instead, Aitchison changes his paintings many times before they are finished. This explains why his favorite models are people who don’t ask to see their pictures while he’s painting them. “If I feel they’re worried and want to look at the painting, I can’t do it.” Since moving to London years ago, he has not felt part of the Scottish painting scene. He says he is not interested in following any tradition, but just paints the way he can. However, his work still influences young British painters. 1. What is the writer trying to do in the text? A. describe popular works by Craigie Aitchison B. teach readers how to paint like Craigie Aitchison C. introduce readers to the artist Craigie Aitchison D. explain how Craigie Aitchison has made money from painting 2. What can the reader learn about Aitchison from the text? A. He works in a different way from other artists. B. He often gets bored with his paintings. C. He improved his drawing by going to art school. D. He did some paintings for the Italian government. 3. What does Aitchison say about his use of color? A. He likes starting with the darkest colors first. B. He knows the colors he’s aiming for when he begins. C. He prefers to paint with yellows, greens, and browns. D. He understands how different colors work together. 4. Aitchison prefers models who don’t A. keep talking to him while he’s working. B. ask him about his strange method of working. C. worry about how long the work will take. D. feel anxious to see the work as it’s developing. 5. What might a visitor at an exhibition say about Aitchison’s work? A. I love his recent paintings of Scotland, which are very similar to a number of other Scottish painters. B. You can still see the influence of his trip to Italy in some of these pictures C. You can tell he spent a lot of time drawing the picture before he started painting. D. I wonder if his law training helps him at all, especially in selling his work . làm cho mình đáp án và dẫn chứng luôn nha mình sẽ vote 5* nhoa năn nỉ lun á
Câu 18 : Cho tập hợp phần tử sau M={1975;1977;1979;...2011} a) tập hợp trên còn mấy phần tử b) tập hợp H={1975;1976} có phải là tập hợp con của tập hợp M không? Vì sao?
Giải giúp em Bài 11 chi tiết với ạ!!!
Read the article and then decide whether the statements are true (T) or (F). After school Kien usually goes swimming. He goes to the swimming pool five times a week. His swimming pool is very good. The pool is 25 metres long and has six lanes. More than a thousand children have swimming lessons there every month. His swimming instructor is experienced and friendly, but she is also strict. She Lessons last 45 minutes, but he usually trains for an hour and a half. During the lesson he swims about two kilometers. His favourite swimming styles are crawl an backstroke. He practices a lot to improve his swimming skills. He wants to achieve good results. Last month he participated in a swimming competition. Ten swimmers from three schools took part in the competition. He won first prize. Swimming is his favourite sport. Swimming is interesting and pleasant, and it helps him to keep fit. True or False? Kien goes to home after school. He practices swimming five times a month. His swimming instructor is so hard. He swims about five kilometers during the lesson. The best friend won first prize in the swimming competition.
Ở ngô gen `B:` thân cao, gen `b:` thân thấp. Hãy XĐ kiểu gen của `P,F_1` và lập SĐL cho mỗi phép lai sau: `a, P:` thân cao `xx` thân thấp `=> F_1: 98` cây thân cao. `b, P:` thân cao `xx` thân thấp `=> F_1: 80` cây thân cao `+80` cây thân thấp. `c, P:` thân cao `xx` thân cao `=> F_1: 86` cây thân cao.
lm hộ bài nối nha mờ thì bảo mk sửa lại sai = vote 2* đúng = 5* + ctlhn + cảm ơn
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