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Trịnh Ngọc Hân cái này không chắc là pải xóa đúng lp
a)\(\sqrt{5}\left(x+2\right)=\sqrt{10}\)
\(\Leftrightarrow x+2=\sqrt{2}\)
\(\Leftrightarrow x=\sqrt{2}-2\)
1. Nam said he was told to be at school before 7 o`clock
2. Hoa said she might visit her parents in the summer
3. The teacher said we could old book for the poor students
4. She said she didn`n buy this bookl
5. The boy said they had to try their best to win this match
6. Her classmate said Lan was the most intelligent girl in their class
11. The teenagers aren’t buying that model these days.
A. That model isn’t being bought by the teenagers these days.
B. That model isn’t bought these days by the teenagers.
C. On these days that model isn’t being bought due to the teenagers.
D. Because of that model isn’t being bought these days by the teenagers
12. People say that he is the most experienced teacher of English.
A. He is said to be the most experienced teacher of English.
B. He is said the most experienced teacher of English.
C. He said the teacher of English is most experienced.
D. That he is the most experienced teacher of English is said by people.
13. People believe that he is a good teacher.
A. It is believed that he was a good teacher. B. He is believed to be a good teacher.
C. They were really believed he is a good teacher. D. He is believed to have been a good teacher.
14. It is thought that he has died a natural death.
A. He is thought to have died a natural death. B. He is thought to be dying a natural death.
C. He is thought to have been dying a natural death. D. He is thought to die a natural death.
15. The coach said, “It’s time for you to go home, boys!”
A. The coach told the boys that it was time for you to go home.
B. The coach tells the boys that it was time for them to go home.
C. The coach told the boys that it is time for them to go home.
D. The coach told the boys that it was time for them to go home.
16.“Why don’t you go with me?” she asked me.
A. He asked me why I don’t go with him. B. He asked me why didn’t I go with him.
C. He asked me why I didn’t go with him. D. He asked me why he didn’t go with me.
17. Why don’t we recycle bottles and cans?
A. We must recycle bottles and cans, mustn’t we? B. What do we recycle bottles and cans for?
C. Shall we recycle bottles and cans? D. How can we recycle bottles and cans?
18. “Why don’t you use the new car, Mr Son?” said Nam.
A. Nam made Mr Son to use the new car. B. Nam asked Mr Son not to use the new car.
C. Nam suggested that Mr Son use the new car. D. Nam suggested that Mr Son uses the new car.
19“Why don’t you use the new car, Mr. Son?” said Nam
A. Nam made Mr. Son to use the new car. B. Nam asked Mr. Son not to use the new car.
C. Nam suggested that Mr. Son use the new car. D. Nam suggested that Mr. Son uses the new car.
20.“You should not lend Susan any more money, Linda” said Nancy.
A. Nancy advised Susan not to borrow any more money from Linda.
B. Nancy advised Linda not to lend Susan any more money.
C. Linda advised Susan not to lend Linda any more money.
D. Nancy advised Linda to lend Susan some more money.
Ta có:a+b=3
<=>\(\left(a+b\right)^2=3^2\)
<=>\(a^2+2ab+b^2=9\)
<=>\(\left(a^2+b^2\right)+2ab=9\)
Vì\(a^2+b^2\)lớn hơn bằng 5 mà \(\left(a^2+b^2\right)+2ab=9\) nên 2ab lớn hơn hoặc bằng 4
Ta lại có:\(P=a^4+b^4+6a^2b^2\)
=\(\left(a^4+2a^2b^2+b^4\right)+4a^2b^2\)
=\(\left(a^2+b^2\right)^2+\left(2ab\right)^2\)
Với mọi giá trị của a;b thì:
\(\left(a^2+b^2\right)^2\)lớn hơn bằng 25;\(\left(2ab\right)^2\)lớn hơn bằng 16
=>\(\left(a^2+b^2\right)^2+\left(2ab\right)^2\)lớn hơn bằng 41
Hay P lớn hơn bằng 41 với mọi a;b
Để P=4 thì \(a^2+b^2=5\) và 2ab=4
Giải tìm a=2 ;b=1 hoặc a=1;b=2
Vậy giá trị nhỏ nhất của P là 41 đạt đc khi và chỉ khi a=2 ;b=1 hoặc a=1;b=2
Làm bừa chả biết đúng hay sai nữa
Ta có:
\(9=a^2+b^2+2ab\ge5+2ab\)
\(\Leftrightarrow ab\le2\)
Ta có:
\(P=a^4+b^4+6a^2b^2\)
\(=\left(a^2+b^2\right)^2+4a^2b^2\)
\(=\left(\left(a+b\right)^2-2ab\right)^2+4a^2b^2\)
Đặt ab = x thì ta có
\(P=\left(9-2x\right)^2+4x^2=8x^2-36x+81\)
\(=\left(8x^2-32x+32\right)+49-4x\)
\(=8\left(x-2\right)^2+49-4x\ge49-4.2=41\)
Dấu = xảy ra khi \(\left\{{}\begin{matrix}ab=2\\a+b=3\end{matrix}\right.\)
Bài 2:
a: \(\sqrt{4x+20}-3\sqrt{x+5}+\dfrac{4}{3}\cdot\sqrt{9x+45}=6\)
\(\Leftrightarrow2\sqrt{x+5}-3\sqrt{x+5}+\dfrac{4}{3}\cdot3\sqrt{x+5}=6\)
\(\Leftrightarrow3\sqrt{x+5}=6\)
=>x+5=4
hay x=-1
b: \(\sqrt{25x-25}-\dfrac{15}{2}\cdot\sqrt{\dfrac{x-1}{9}}=6+\sqrt{x-1}\)
\(\Leftrightarrow5\sqrt{x-1}-\dfrac{15}{2}\cdot\dfrac{\sqrt{x-1}}{3}-\sqrt{x-1}=6\)
\(\Leftrightarrow\sqrt{x-1}\cdot1.5=6\)
=>x-1=16
hay x=17