Bài 1:

A= \(4\sqrt{20}+2\sqrt{45}-8\sqrt{5}+2\sqrt{180}\)

= \(4\sqrt{4.5}+2\sqrt{9.5}-8\sqrt{5}+2\sqrt{36.5}\)

= \(8\sqrt{5}+6\sqrt{5}-8\sqrt{5}+12\sqrt{5}\)

= \(\left(8+6-8+12\right)\sqrt{5}\)

= \(18\sqrt{5}\)

B= \(\dfrac{1}{\sqrt{5}+\sqrt{7}}-\dfrac{1}{\sqrt{5}-\sqrt{7}}\)

= \(\dfrac{\left(\sqrt{5}-\sqrt{7}\right)-\left(\sqrt{5}+\sqrt{7}\right)}{\left(\sqrt{5}+\sqrt{7}\right)\left(\sqrt{5}-\sqrt{7}\right)}\)

= \(\dfrac{\sqrt{5}-\sqrt{7}-\sqrt{5}-\sqrt{7}}{\sqrt{5^2}-\sqrt{7^2}}\)

= \(\dfrac{-2\sqrt{7}}{5-7}\)

= \(\dfrac{-2\sqrt{7}}{-2}\)

= \(\sqrt{7}\)

C= \(\sqrt{\dfrac{4+\sqrt{7}}{4-\sqrt{7}}}+\sqrt{\dfrac{4-\sqrt{7}}{4+\sqrt{7}}}\)

= \(\sqrt{\dfrac{\left(4+\sqrt{7}\right)^2}{\left(4-\sqrt{7}\right)\left(4+\sqrt{7}\right)}}+\sqrt{\dfrac{\left(4-\sqrt{7}\right)^2}{\left(4+\sqrt{7}\right)\left(4-\sqrt{7}\right)}}\)

= \(\sqrt{\dfrac{\left(4+\sqrt{7}\right)^2}{4^2-\sqrt{7^2}}}+\sqrt{\dfrac{\left(4-\sqrt{7}\right)^2}{4^2-\sqrt{7^2}}}\)

= \(\sqrt{\dfrac{\left(4+\sqrt{7}\right)^2}{9}}+\sqrt{\dfrac{\left(4-\sqrt{7}\right)^2}{9}}\)

= \(\dfrac{\sqrt{\left(4+\sqrt{7}\right)^2}}{\sqrt{9}}+\dfrac{\sqrt{\left(4-\sqrt{7}\right)^2}}{\sqrt{9}}\)

= \(\dfrac{\left|4+\sqrt{7}\right|}{3}+\dfrac{\left|4-\sqrt{7}\right|}{3}\)

= \(\dfrac{\left(4+\sqrt{7}\right)+\left(4-\sqrt{7}\right)}{3}\)

= \(\dfrac{8}{3}\)

D= \(\sqrt{5+\sqrt{21}}+\sqrt{5-\sqrt{21}}\)

\(\Rightarrow D^2=\left(\sqrt{5+\sqrt{21}}+\sqrt{5-\sqrt{21}}\right)^2\)

= \(\left(\sqrt{5+\sqrt{21}}\right)^2+2.\sqrt{5+\sqrt{21}}.\sqrt{5-\sqrt{21}}+\left(\sqrt{5-\sqrt{21}}\right)^2\)

= \(\left|5+\sqrt{21}\right|+2\sqrt{\left(5+\sqrt{21}\right)\left(5-\sqrt{21}\right)}+\left|5-\sqrt{21}\right|\)

= \(5+\sqrt{21}+2\sqrt{25-21}+5-\sqrt{21}\)

= \(10+2\sqrt{4}\)

= 10+4=14

Bài 2:

\(\sqrt{xy}+1+\sqrt{x}+\sqrt{y}\)

= \(\left(\sqrt{xy}+\sqrt{x}\right)+\left(\sqrt{y}+1\right)\)

= \(\sqrt{x}\left(\sqrt{y}+1\right)+\left(\sqrt{y}+1\right)\)

= \(\left(\sqrt{y}+1\right)\left(\sqrt{x}+1\right)\)

16. We started learning English 4 years ago.

17. My father has given up smoking since last year.

18. They started working in that factory in 2001.

19. Lan didn't write to Mary a month ago.

20. He started living in HN when he was 12.

21. I didn't see her a long time ago.

22. How long ago did you learn French.

23. How long have you listened to classical music.

24. I haven't seen her for 10 years.

25. When did you buy this car.

26. It's two years since we visited Kuala Lumpur.

27. Mai has sung since she was eleven.

28. Is it the cheapest computer do you have?

Happy New Year 2012 qua lâu rồi bạn phải là Happy New Year 2016

The test is easy to do it in fifteen minutes.

III,

1, We will travel Nha Trang next week.

2, Nga and Lan will visit their grandparents.

3, They will go to the movie tonight.

4, Hoa will have lots of friends soon.

5, I will come after lunch.

6, He will see you tomorrow afternoon.

7, My father will be free at 7:30 this evening.

8, The students will go camping next Sunday.

IV,

1, Will/will

2, Will/won't

3, Will/won't

4, Will/will

5, Will/won't

6, Will/will

7, Will/won't

8, Will/will

V,

2, What

3, Who

4, Where

5, What time

6, How

7, When

8, Why

9, Where

VI,

2- Hello. Can I speak to Trang.

3- I'm sorry. She's out at the moment. Who's calling?

4- This is Nga. When will she come back?

5- She'll be back at about half past six.

6- All right. Please tell her I'll call again at seven.

7- Ok. I'll tell her.

8- Bye.

VII,

1, Is

2, Who

3, Will

4, Would

5, Where

6, When

7, at

8, see

B,

I,

1, January

2, February

3, March

4, April

5, May

6, June

7, Juny

8, August

9, September

10, October

11, November

12, December

II,

2^nd: second

3^rd: third

5^th: fifth

9^th: ninth

12^th: twelfth

19^th: nineteenth

20^th: twentieth

21^st: twenty- first

27^th: twenty- seventh

30^th: thirtieth

32^nd: thirty- second

II,

1, September 19^th

2, May 2^nd

3, October 21^st

4, July 35^th

5, December 12^th

6, February 8^th

II,

1, jogs

2, will visit

3, will be

4, live

5, will have

6, brushes

7, will come

8, Will she have

9, will invite

10, meet

(1+2x)(1-2x)-x(x+2)(x-2)

= [1²-(2x)²]-x(x²-2²)

= (1-4x²)-x(x²-4)

= (1-4x²)-(x³-4x)

= 1-4x²-x³+4x

= (1-x³)-(4x²-4x)

= -(x³-1)-(4x²-4x)

= -(x-1)(x²+x+1)-4x(x-1)

= -(x-1)(x²+x+1+4x)

= -(x-1)(x²+5x+1)

vào câu hỏi tương tự nha bạn

tick cho tui nha

phần A chép đúng đầu bài hả bn

2x²=x

\(\Leftrightarrow2x^2-x=0\)

\(\Leftrightarrow x\left(2x-1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\2x-1=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\2x=1\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{1}{2}\end{matrix}\right.\)

Vậy x=0 hoặc x=\(\dfrac{1}{2}\)

(Bạn tính phép chia trước sau đó mới tìm a nha bạn)

Để \((2x^3-3x^2+x+a)⋮\left(x+2\right)\) thì a-30=0

\(\Leftrightarrow a=30\)

Vậy a=30 thì (2x³-3x²+x+a)\(⋮\) (x+2)