Tìm gtnn của (x+y)^2+(yy-2/3)^2-2020
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14 tháng 2 2020
a) Xét ▲OAD và ▲OBC có :
OA = OB ( gt )
góc COD chung
OC = OD ( gt )
=> ▲OAD = ▲OBC ( c-g-c )
=> đpcm
b) Gọi giao điểm của BC và AD là M
Vì ▲OAD = ▲OBC ( c/m trên )
=> góc OCB = góc ODA ( 2 góc tương ứng )
Xét ▲ACM có góc MAC + góc ACM + góc CMA = 1800
Xét ▲BMD có góc BMD + góc MDB + góc DBM = 1800
Mà góc OCB = góc ODA ( c/m trên ) và góc CMA = góc BMD ( đối đỉnh )
=> góc CAM = góc MBD ( đpcm )
BT
1
14 tháng 2 2020
| 3x - 2 | - 2x = -1
| 3x -2 | = -1 + 2x
TH1 : 3x - 2 = -1 + 2x
3x - 2x = -1 + 2
x = 1
TH2 : 3x - 2 = 1 - 2x
3x + 2x = 1 + 2
5x = 3
x = 3/5
Vậy x=1 hoặc x = 3/5
Hok tốt!!!!!
HT
2
13 tháng 2 2020
Mình có 2 mẫu :
Mẫu 1 : My favourite hobby is reading. I enjoy reading a book when I am free. I started to do it when I was four years old. The first time I did it, I felt interested. So I kept reading. The teachers always taught me to read the difficult words. I was happy when I read a story with a happy ending. I was thrilled when I read a detective story. I enjoy reading because I to explore the imaginative world of my favourite author, J.K.Rowling who writes “ Harry Potter” . There are a lot of advantages of reading. Reading can make me relaxed and calm. I can also learn new vocabulary items. Then I can further improve my English. Moreover, it can give me an unlimited imagination, so I can write books in the future. I can learn the different cultures and customs of other countries in the world too. I read at least one hour every day. I read books by myself. I usually read it at home. I wish I could read different kinds of books because it might be very challenging.
Mẫu 2 : I have many hobbies, but I reading most. Books are always a good friend to me. It is a good way to improve my vocabularies by exposing many new words.I star to reading book when i in grade 3.my brother inspired me to do that.I usualy share my hobby with my friend and my english teacher.By reading, I get better at concentration because it requires me to focus on what I am reading for long periods. It also opens up the knowledge door for me. Reading books tell me about the world's history, let me see the structure of the brain, or bring me a story of Sherlock Holmes. I think reading is one of the most interesting indoors activity and I will keep this hobby forever.
nha !!!