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12 tháng 1
a: Ta có: \(\widehat{ABC}=\widehat{ACB}\)(ΔABC cân tại A)
\(\widehat{ACB}=\widehat{ECN}\)(hai góc đối đỉnh)
Do đó: \(\widehat{ABC}=\widehat{ECN}\)
Xét ΔMBD vuông tại D và ΔNCE vuông tại E có
BD=CE
\(\widehat{MBD}=\widehat{NCE}\)
Do đó: ΔMBD=ΔNCE
=>DM=EN
b: Ta có: DM\(\perp\)BC
EN\(\perp\)BC
Do đó: DM//EN
Xét ΔIDM vuông tại D và ΔIEN vuông tại E có
MD=EN
\(\widehat{MDI}=\widehat{ENC}\)(hai góc so le trong, DM//EN)
Do đó: ΔIDM=ΔIEN
=>IM=IN
=>I là trung điểm của MN
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MN
23 tháng 1 2021
My mother is a person I admire most. She devoted a lot of time and energy to the upbringing of my two brothers and I. Despite working hard, she always made time to teach us many useful things which are necessary and important in our later lives. Moreover, she is a good role model for me to follow. She always tries to get on well with people who live next door and help everyone when they are in difficulties, so most of them respect and love her. I admire and look up to my mother because she not only brings me up well but also stands by me and gives some help if necessary. For example, when I encounter some difficulties, she will give me some precious advice to help me solve those problems. She has a major influence on me and I hope that I will inherit some of her traits.
23 tháng 1 2021
This year my grandmother is over seventy years old. She still looks healthy because she keeps the habit of walking every morning. Her face was plump and kind. Her gray-brown eyes were always a gentle, warm glow. Her hair was waist-length, more white than half. My grandmother is also a person who loves her children deeply. I have grown up with the sweet apathy she lulled, with so many wonderful fairy tales she tells. Every night, her skinny, wrinkled hands patted me back to sleep. I really love this kind of my grandmother. I wish she was always healthy to live happily with her children and grandchildren.
TP
20 tháng 4 2018
Technology is now a big part of our society and our predictable future. There is little room for people who wish to live without technology, and luckily, it is still advancing at a rate that has helped stave off stagnation. I believe that for every advantage that technology brings us, it also brings us a disadvantage at the same time.
Smartphones enable people to stay in touch, even over long distances, and they are relatively safe and reliable to use. There are devices that people can use to communicate with plus at the other end of the planet and getting and keeping in touch with other people is very easy.
The disadvantages of smartphone is that it means people no longer need to meet in person as much, and interpersonal relationships are suffering worldwide because people are communicating through a small handheld device. A lot of people have smartphones and they use them almost semi-continuously, including in public settings when they could be making new friends, finding new lovers, and interacting with their current friends.
The advantages of the internet are that people can communicate over vast distances and can gain access to information and get answers to their questions very quickly. The disadvantage is that the Internet isn’t moderated in the way that people think and lots of it is filled with misinformation and outright lies.
Even brand-named websites which have a lot of trust are not accountable for what appears on their own websites. Even respected and branded news sites have stories that have passed through many people’s hands and originally started as lies with zero accountability throughout the dissemination process.
In conclusion, technology brings about such a lot of advantages. However, it’s people’s duty to use it in an appropriate way to make it beneficial
28 tháng 6 2020
Bổ sung thêm điều kiện: a,b,c>0 thì mới có bất đẳng thức trên nhé.
Khi đó:
\(a\left(\frac{b}{c}+\frac{c}{b}\right)\ge2a\)
\(\Leftrightarrow\frac{b}{c}+\frac{c}{b}\ge2\)
Dễ thấy bđt trên đúng theo bđt AM-GM cho hai số dương \(\frac{b}{c},\frac{c}{a}\)
Hoặc biến đổi tương đương, chuyển 2 sang vế trái ta được:
\(\frac{\left(b-c\right)^2}{bc}\ge0\)(Luôn đúng)
Dấu "=" khi b=c.
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