Bài 1: Cho hình thang ABCD, (AB//CD), AB = a, CD = b. Hai đường chéo cắt nhau tại I. Qua I kẻ EF//AB cắt hai cạnh bên tại E, F a/ Chứng minh IE = IF b/ Tính EF theo a và b Bài 2: Kẻ đường cao BD và CE của tam giác ABC và các đường cao DF và EG của tam giác ADE. a/ Chứng minh hệ thức AD.AE= AC.AF b/ Chứng minh FG//BC

Các câu hỏi liên quan

I. Choose the word that has the underlined part pronounced differently from the others. 1.​A. vanilla​B. vacuum​C. add​D. facsimile 2.​A. whiten​B. fiber​C. zipper​D. conveyor 3.​A. remove​B. wrote​C. mold​D. cocoa 4.​A. follow​B. powder​C. show​D. borrow 5.​A. wood​B. thousand​C. procedure​D. hairdryer B. VOCABULARY AND GRAMMAR III. Complete the sentences with the correct verb form in the bracket. 1.​You would hear my explanation if you (not talk) ​​​ so much. 2.​What you (do) ​​​ if you hear the burglar alarm? 3.​If you (read) ​​​ the instructions carefully, you wouldn’t have answered the wrong question. 4.​If Mel (ask) ​​​ her teacher, he’d have answered her questions. 5.​I would repair the roof myself if I (have) ​​ a long ladder. 6.​Unless they turn that radio off, I (go) ​​​ mad. 7.​If you were made redundant, what you (do) ​​​? C. READING III. Choose the word or phrase among A, B, C or D that best fits the blank space in the following passage. ​Have a walk (1) ​​ a beach, listen to the sound of the sea waves, and suddenly you see a lot of rubbish on the beach. Pollution takes away all the (2) ​​ of our beaches. I feel really annoyed (3) ​​ I see plastic bags lying on the sand, cigarette ends buried in the sand, and soda cans floating in the sea. ​There are a lot of things that we can do. (4) ​ we see rubbish, we should do our part in the protecting the land (5) ​ picking it up and throwing it in dust bins. (6) ​, we can form some kind of organization that helps (7) ​​ the beaches. If everyone does their part, the beaches will be a wonderful and beautiful place. We need to start now (8) ​​ the beaches are damaged beyond repair. 1.​A. on​B. in​C. at​D. over 2.​A. beauty​B. beautifully​C. beautiful​D. being beautiful 3.​A. before​B. after​C. when​D. while 4.​A. While​B. Soon​C. Unless​D. If 5.​A. by​B. with​C. of​D. in 6.​A. Nevertheless​B. Moreover​C. However​D. Therefore 7.​A. cleaning up​B. cleaning up​C. clean up​D. clean off 8.​A. when​B. after​C. until​D. before