Trên tia đối tia $DC$ lấy $E$ sao cho $DE=BM$
Dễ chứng minh được tam giác ABM=tam giác ADE
nên $AM=AE$ và $\widehat{EAD}=\widehat{MAB}$
Mà $\widehat{MAB}+\widehat{DAM}=90^o$
Nên $\widehat{EAD}+\widehat{DAM}=90^o$
vì vậy tam giác EAN vuông tại $A$
Áp dụng hệ thức lượng trong tam giác vuông có:
$(\dfrac{1}{AD})^2=\dfrac{1}{AE^2}+\dfrac{1}{AN^2} \geq \dfrac{2}{AM.AN}$
Nên $AM.AN \geq 2.AD^2=2a^2$
Dấu $=$ xảy ra $⇔AM=AN⇔M≡C$
Đáp án + giải thích các bước giải:
Qua `A` kẻ đường thẳng vuông góc với `AM`, đường thẳng này cắt `CD` tại `E`
Xét `ΔADE` và `ΔABM`, có:
`+) \hat{ADE}=\hat{ABM}`
`+) AD=AB`
`+) \hat{EAD}=\hat{MAB}` (cùng phụ `\hat{DAM}`)
`->ΔADE`$\backsim$`ΔABM`
`->AE=AM`
Xét `ΔAEN` vuông tại `A` có đường cao `AH`, có:
`1/(AD)^2=1/(AE)^2+1/(AN^2)`
`->1/a^2=1/(AM^2)+1/(AN)^2>=2\sqrt{1/(AM.AN)^2}`
`->1/a^2>=2/(AM.AN)`
`->AM.AN>=2a^2`
Dấu bằng xảy ra khi `AM=AN`
`->M≡N≡C`
quy đồng phân thức (3/x^3+8);(1/4x+8)
nêu dãy hoạt động hóa học kim loại đầy đủ
yeah >< đc vào BĐHH rồi :D VẼ ANIME / CHIBI / CÁI GÌ CŨNG ĐC :>
mn giúp em với ạ Hỗn hợp X gồm axit no đơn chức mạch hở và hai ancol no đơn chức mạch hở đồng đẳng kế tiếp của nhau. Chia X làm 3 phần bằng nhau. Cho phần 1 tác dụng với lượng dư Na, khi phản ứng xảy ra hoàn toàn thu được 3,92 lít H2 ( đktc). Để trung hòa lượng axit trong phần 2, cần 200 ml dung dịch NaOH 1M. Đun nóng phần 3 với một lượng H2SO4 đặc, rồi thực hiện phản ứng este hóa với hiệu suất phản ứng là 60%, ta thu được 7,29 gam este. Biết tốc độ phản ứng của các ancol là như nhau. Có bao nhiêu axit thỏa mãn điều kiện?
Encouraging children to eat and drink is very important. (health)
Mn giải giúp mik bài này vs.Hứa đánh giá 5 sao
làm ơn giúp e có đc ko zậy :((((
21. Because of the development of birth-control, women could delay having children . A. Because birth-control was developed, women could delay having children. B. Because birth-control is developed, women could delay having children. C. Despite birth-control is developed, women could delay having children. D. Though birth-control was developed, women could delay having children. 22. John is fat because he eats so many chips. A. John is fat because of the fact that he eats so many chips. B. John is fat because of eating so many chips. C. John is fat because of not eating so many chips. D. A & B are correct. 23. He was very tired but he kept on working. A. Despite he was very tired, he kept on working. B. In spite of he was very tired, he kept on working. C. Though his tiredness, he kept on working. D. Although he was very tired, he kept on working. 24. The trip was boring but we enjoyed it a lot. A. We enjoyed boring trips. B. We are bored with the trip. C. We liked the trip very much even though it was boring. D. The trip bored us. 25. Because the medical care is improved, we live healthier. A. Because of the medical care is improved, we live healthier B. Because of the improvement of the medical care, we live healthier. C. Despite the improvement of the medical care, we live healthier. D. B & C are correct. 26. Although he is rich, he feels unhappy. A. He feels unhappy because of his richness. B. He feels unhappy, so he is rich. C. Despite his richness, he feels unhappy. D. He feels unhappy because he is rich. 27. She accepted the job because the salary was high. A.She accepted the job because of the high salary. B. She accepted the job because of the salary. C. She accepted the job in spite of the high salary. D. All are correct. 28. We can study although it is noisy. A. We can study despite of the noise. B. We can study in spite of the noise. C. We can study despite the fact that it is noisy. D. B & C are correct. 29. People want to learn English because it is important. A. Because of its importance, people want to learn English. B. People want to learn English, so it is important. C. Despite its importance, people want to learn English. D. People want to learn English though it is important.. 30. Despite the fact that it was snowing, I felt warm. A. In spite of snowing, I felt warm. B. In spite of feeling warm, it was snowing. C. Although it was snowing, I felt warm. D. Although I felt warm, it was snowing.
Các bạn cho mk hỏi như thế nào thì được coi là đầy đủ Hag+Layer từ màn vẽ vậy ạ? Có ảnh chi tiết nha Calli: Trang (digi) - Đổ bóng,nền caro, tone xanh dương ạ
Loga.vn - Cộng Đồng Luyện Thi Trực Tuyến
