Cho x, y > 0 va x + y <= 1 . Chung minh rang :\(\frac{1}{x^2+xy}+\frac{1}{y^2+xy}\ge4\)
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23 tháng 10 2020
1. I was stuck at that traffic jam for hours! ...I've been stuck in traffic for hours!..................
2. There were no clouds on the sky .........No clouds in the sky .....................
3. Matthew was in work when I called ..........Matthew was working when I called ...............
4. Megan will be on the office from nine to four. ............Megan will be in the office from nine to four hours. ...................
5. Rachel is to her desk .............Rachel arrives at her desk .................
6. There will be many new people on the party .........There will be many new people at the party .................................
7. The food is in the table ........Food on the table .......................
8The keys were not to his pocket. ............The key is not in his pocket. .......................
9. She looked in herself and smiled happily ..........She looked at herself and smiled happily ..................
10. The books were at the shelf ...........the books are already on the shelf....................
Tự làm nên ko biết đã đúng chưa đâu -.-"
23 tháng 10 2020
3n3n ⋮⋮ n−1n−1
⇒3(n−1)+3⇒3(n−1)+3 ⋮⋮ n−1n−1
Do 3(n−1)3(n−1) ⋮⋮ n−1⇒3n−1⇒3 ⋮⋮ n−1n−1
⇒n−1∈Ư(3)={±1;±3}⇒n−1∈Ư(3)={±1;±3}
Với n−1=−1⇒n=0n−1=−1⇒n=0
n−1=1⇒n=2n−1=1⇒n=2
n−1=−3⇒n=−2n−1=−3⇒n=−2
n−1=3⇒n=4n−1=3⇒n=4
Vậy n={0;±2;4}
23 tháng 10 2020
1 Complete the sentences withmissing preposition of place.
1 My mother's portrait is in the fireplace.
2 Is.the left there is a window
3 We had dinner is a very nice restaurant.
4 The dinner will be for .Mark's
5 The cat is sleeping on the sofa
6. A big lamp is hanging on the table.
7 The taxi will be waiting at the hotel.
8. There is a beautifful garden right the back of the house.
9 Go the left you can see a monument
10. He was sitting at the top of the stairs
23 tháng 10 2020
1 Complete the sentences withmissing preposition of place.
1 My mother's portrait is...ON...................the fireplace.
2.............................the left there is a window
3 We had dinner..............IN..........a very nice restaurant.
4 The dinner will be ...............Mark's
5 The cat is sleeping..ON........the sofa
6. A big lamp is hanging..........BEHIND......the table.
7 The taxi will be waiting................the hotel.
8. There is a beautifful garden...................the back of the house.
9.......................the left you can see a monument
10. He was sitting.................the top of the stairs
CÁI NÀY LÀ THÊM NƠI CHỐN MÀ NHỈ ==" SAO THÊM VÀO THẤY KO HỢP LÝ CẬU Ạ ==' CÓ THIẾU ĐỀ KO?
nhưng cũng có khản năng tớ ngốc :"
23 tháng 10 2020
1 Complete the sentences withmissing preposition of place.
1 Who is that boy sitting.....with...........Ann and Liz?
2 There were many beautiful flowers......in...the garden.
3. We used to live.....on..........the third floor.
14 Bob is writing ......on...the copy book
15. There is such a mess.....in.......the kitchen!
9 A lot of stars are..with.....us
2 tháng 11 2020
Circle the correct answer
1,We can't go out because it.........now.
A,am raining B,is raining C,are rainig D,rains
2,Lam..........lunch with classmate right now.
A, have B,has C,is having D,are having
3,The dog is in........the computer
A,next to B,between C,behind D,front of
choose the corect word A, B or C to fill each black in the following consversation.
Mum: We are moving to the new a partment next month. Do you want to have a new bed?
Mi : No,I don't Mum.I (1).......my old bed. It's so comfortabl. But can I (2)..... a new poster ?
Mum: You have three postert alrealy. You an put them (3)......the wall in your new room.
Mi :Yes, Mum.I want to have a family photo on my desk. There (4)......only a lamp on it now.
Mum: That's a good idea!.Oh,where do you want to put your desk?
Mi : (5).......to my bed,Mum. I also want to a small plant in my room.
Mun: That's fine. It can go (6)......the bookshelf anh=d the desk.
1, A, hate B,dis C,love
2, A,sall B,buy C,give
3, A,near B,in C,on
4, A,is B,are C,isn't
5, A,next B,behind C,near
6, A,next to B,between C,in front of
LP
23 tháng 10 2020
Circle the correct answer
1. B
2.C
3.D
Choose the correct word
1.C
2.B
3.C
4.A
5.A
6.B
Áp dụng bất đẳng thức Cauchy–Schwarz dạng Engel ta có :
\(\frac{1}{x^2+xy}+\frac{1}{y^2+xy}\ge\frac{\left(1+1\right)^2}{x^2+xy+y^2+xy}=\frac{4}{\left(x+y\right)^2}\)
Cần chỉ ra \(\frac{4}{\left(x+y\right)^2}\ge4\)
Ta có : \(x+y\le1\)
=> \(\left(x+y\right)^2\le1\)
=> \(\frac{1}{\left(x+y\right)^2}\ge1\)( nghịch đảo )
=> \(\frac{4}{\left(x+y\right)^2}\ge4\)( nhân 4 vào cả hai vế )
=> đpcm
Đẳng thức xảy ra <=> x = y = 1/2