Cho hình thang cân ABCD(AB//CD,AB<CD).Kẻ đường caoAE,BF của hình thang.Chứng minhDE=CF

8. Đốt cháy hoàn toàn 6 mg một chất hữu cơ X trong oxi dư thu được 4,4 mg CO2 và 3,6 mg H2O. Mặt khác, oxi hoá hoàn toàn 9,0 mg X bằng CuO dư thu được 3,36 ml khí N2 (đktc). Kết luận nào sau đây là không đúng? A. %C = 20%. B. %H = 6,67%. C. %N = 46,67%. D. %O = 13,33%.

Choose the best option to finish each sentence Giải thích tại sao chọn câu đó dùm mình với 1. When he ......... into the office, the secretary .... a crosswords puzzle. A. came/ was doing B. was coming/ was doing C. was coming/ did D. came/ did 2. Why ....to me while I .......? A. did you not listen/ was speaking B. were you not listening/ was speaking C. were you not listening/ spoke D. did you not listen/ spoke 3. While I .....for him to call up, he ..... a good time in the bar. A. waited/ was having B. have waited/ was having C. was waiting/ have had D. was waiting/ was having 4. They ...... this film lately. A. have seen B. saw C. have been seeing D. were seeing 5. She ........ the picture when I came. A. painted B. has painted C. was painting D. have been 6. She .......a bath at seven o’clock last night. A. was having B. had C. has had D. has been having 7. She ......dishes already. A. was washing B. washed C. has washed D. has been washing 8. They .... supper when the telephone rang. A. had B. have had C. were having D. have been having 9. I ..... you for ages. A. didn’t meet B. haven’t met C. was not meeting D. haven’t been meeting 10. Last summer he ..... to Ha Long Bay. A. has gone B. was going C. went D. has been going

câu 1 : ( 2x+3) (x+4) câu 2 : (3x-8) (4x+1) câu 3 : (2+3x) (3x-2)-(3x-4)^2 Mng giải giúp em với ạ

x–3^2+6xy–3y^2 thành nhân tử ta được

V9x-27 -V4x-12 =3 làm giúp em với ạ

mọi người giúp em với em gấp lắm ạ hứa sẽ vote 5 sao

giúp mình với,mình đang cần gấp gấp gấp ạ

Giúp vs ah ................................

nguyên tử B có tổng số các hạt là 28 trong đó số hạt mang điện chiếm 35,7%. Hãy xác định số p, số n và số e trong nguyên tử B