cho tam giác abc có các trung tuyến ae, bf, ch cắt nhau tại g . a,chứng minh tam giác abc và efh đồng dạng .b, g là trọng tâm tam giác efh

a) A=3-3^2+3^3-3^4+.......+3^2019-3^2020 b) B=1-3+5-7+9-11+......+2013-2015

Một vật có khối lượng 2kg chịu tác dụng của một lực: F = 10(N) có phương hợp với độ dời trên mặt phẳng nằm ngang một góc: α = 45°. Giữa vật và mặt phẳng có hệ số ma sát µ = 0,2 . Lấy g = 10m/s2 a. Tính công của ngoại lực tác dụng lên vật khi vật dời một quãng đường 2m. Công nào là công dưong, công âm? b. Tính hiệu suất trong trường hợp này

Viết 1 đoạn văn ngắn khoảng 8 đến 10 câu tả cảnh thiên nhiên quê em , sử dụng 1 câu đặc biệt , 1 câu rút gọn . Gạch chân các câu đó

Giải thích lời khuyên của Lênin: "Học,học nữa , học mãi"

khi chiếu ánh sáng với cường độ như nhau vào các cây A,B,c nhận thấy cây A không thải cũng không hấp thu CO2, cây B hấp thụ CO2, Cây C thải CO2. Hãy cho biết cây A,B,C thuộc nhóm thực vật nào?????

Tìm mđể phương trình x^2 -2(m-2)x+m-3=0 có một nghiệm thuộc khoảng (1;2)và nghiệm kia nhỏ hơn 1

Choose the correct answers. 23. He broke my watch. A. My watch were broken. B. My watch be broken. C. My watch is broken. D. My watch was broken. 24. The teacher explained the rule to the student. A. The rule was explained to the student. B. The students were explained the rule. C. The students were explained the rules. D. A and B are correct 25. He often asks me to help him. A. He is often asked to help them. B. They are often asked to help me. C. I am often asked to help him. D. I am often asked him to help me. 26. His friends never forgave his betrayal. A. His betrayal were never forgiven by his friends. B. His betrayal was never forgiven by his friends. C. His betrayal was never forgave by his friends. D. His betrayal never forgave by his friends. 27. I am sure we’ll settle the matter easily. A. I’m sure the matter will settle easily. B. I’m sure the matter will be settled easily. C. I’m sure the matter will settled easily. D. I’m sure the matter won’t be settled easily. 28. They speak much about this book. A. This book is much spoken about. B. This book is much spoken. C. This book is much about spoken. D. This book are much spoken about. 29. Have they tested all the machines? A. Have all the machines be tested? B. Have all the machines been testing? C. Have all the machines been tested? D. Have all the machines been being testing? 30. Does he realize that they are laughing at him? A. Is he realized that he is laughing at? B. Is he realized that he is being laughed at? C. Does he realize that he is laughing at? D. Does he realize that he is being laughed at? 31. The manager offers me several jobs. A. I was offers several jobs. B. I am offered several jobs. C. Several jobs are offered to me. D. B and C are correct. 32. We found that they had cancelled the soccer match. A. We found that the soccer match had been cancelled. B. The soccer match had been cancelled. C. The soccer match was found that had been cancelled. D. The soccer match was found to have been cancelled by us. 33. Mary is cutting a cake with a sharp knife. A. A cake is being cut with a sharp knife by Mary. B. A sharp knife is cutting a cake and Mary. C. Mary and a sharp knife are cutting a cake. D. Mary is cutting a sharp knife by a cake. 34. “Did Shakespeare write this play?” A. Did this play be written by Shakespeare? B. Was this play written by Shakespeare? C. This play was written by Shakespeare. D. Did this play Shakespeare write? 35. Which book do the students love? A. Which book are done love by the students? B. Which book is the students loved? C. Which book are loved by the students? D. Which book is loved by the students?

Giới thiệu về một danh lam thắng cảnh ở quê hương em . Quê mik ở Hà Nội nhé . CẢM ƠN trước

Trong tinh thể các hạt (nguyên tử, phân từ, ion) A. dao động nhiệt xung quanh vị trí cân bằng. B. đứng yên tại những vị trí xác định. C. chuyển động hỗn độn không ngừng. D. chuyển động trên quỹ đạo tròn xung quanh một vị trí xác định.