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21 tháng 1 2022
\(A=x+\dfrac{1}{x-2}\\ \Rightarrow A=x-2+\dfrac{1}{x-2}+2\)
Áp dụng BĐT Cô-si ta có:
\(A=x-2+\dfrac{1}{x-2}+2\\ \ge2\sqrt{\left(x-2\right).\dfrac{1}{x-2}}+2\\ =2\sqrt{1}+2\\ =4\)
\(\text{Dấu "=" xảy ra}\Leftrightarrow x-2=\dfrac{1}{x-2}\\ \Leftrightarrow\left(x-2\right)^2=1\\ \Leftrightarrow\left[{}\begin{matrix}x-2=1\\x-2=-1\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=3\left(tm\right)\\x=1\left(ktm\right)\end{matrix}\right.\)
Vậy \(A_{min}=4\Leftrightarrow x=3\)
21 tháng 1 2022
\(A=x-2+\dfrac{1}{x-2}+2\ge2+2=4\)
Dấu '=' xảy ra khi x-2=1 hoặc x-2=-1
=>x=3 hoặc x=1
17 tháng 7 2017
~Find mistake~
IV)
1: B=>Taken
2:C=>Be answered
3:A=>He
4:B=>Believed
5:C=>Been repaired
6:B=>had been found
7:C=>Impressed
8:A=>am helped
9:A=>weren't tell
10:B=>Repaired
V) REWRITE SENTENCE
P/s: bạn chụp làm mk nhìn đến nghẹo cổ mất,mk ghi ý chính ra,còn lại .... bạn tự biết ghi j bạn nhé .
1.Some photos are going to be taken by Lan....
2:The road isn't going to be widened.....
3:Your book needs opening/to be opened....
4:I used to be given a nice present by Tom...
5:The mixture ought to be shaked well ...
6:All the cakes ought to have been made...
7:Some new workers have to be taken on...
8:The kites have to be flown....
9:A lot of new things had to be bought..
10:He is said to be a liar.
11:The earth is believed to be rough and flat.
12:He is all known to be working for...
13:Mr.smith is thought to have just proposed...
14:He is supposed to have been running...
15:Whales are said to be hunted...