representatives

natural - include

recycling

mixture

environmentally

packaging

open your book

mở sách xem phần ghi nhớ

1.........................................

=>the computer hasn't been fixed by them yet

2.......................................

=>Last night I was helped by a stranger.

3: \(\left(\dfrac{1}{\sqrt{2}-1}-\dfrac{1}{\sqrt{2}+1}\right):\sqrt{3-2\sqrt{2}}\)

\(=\dfrac{\sqrt{2}+1-\sqrt{2}+1}{2-1}:\left(\sqrt{2}-1\right)\)

\(=\dfrac{2}{\sqrt{2}-1}=2\left(\sqrt{2}+1\right)=2\sqrt{2}+2\)

5: 

\(\dfrac{\sqrt{5}+\sqrt{3}}{\sqrt{5}-\sqrt{3}}+\dfrac{\sqrt{5}-\sqrt{3}}{\sqrt{5}+\sqrt{3}}\)

\(=\dfrac{\left(\sqrt{5}+\sqrt{3}\right)^2+\left(\sqrt{5}-\sqrt{3}\right)^2}{\left(\sqrt{5}-\sqrt{3}\right)\left(\sqrt{5}+\sqrt{3}\right)}\)

\(=\dfrac{8+2\sqrt{15}+8-2\sqrt{15}}{2}=\dfrac{16}{2}=8\)

6:

\(\dfrac{\sqrt{5}-1}{\sqrt{5}+1}-\dfrac{\sqrt{5}+1}{\sqrt{5}-1}\)

\(=\dfrac{\left(\sqrt{5}-1\right)^2-\left(\sqrt{5}+1\right)^2}{\left(\sqrt{5}+1\right)\left(\sqrt{5}-1\right)}\)

\(=\dfrac{6-2\sqrt{5}-6-2\sqrt{5}}{4}=\dfrac{-4\sqrt{5}}{4}=-\sqrt{5}\)

4:

\(\dfrac{6}{\sqrt{2}-\sqrt{3}+3}\)

\(=\dfrac{6\left(\sqrt{2}-\sqrt{3}-3\right)}{\left(\sqrt{2}-\sqrt{3}-3\right)\left(\sqrt{2}-\sqrt{3}+3\right)}\)

\(=\dfrac{6\left(\sqrt{2}-\sqrt{3}-3\right)}{5-2\sqrt{6}-9}=\dfrac{-6\left(\sqrt{2}-\sqrt{3}-3\right)}{4+2\sqrt{6}}\)

\(=\dfrac{-3\left(\sqrt{2}-\sqrt{3}-3\right)}{\sqrt{6}+2}=\dfrac{-3\left(\sqrt{2}-\sqrt{3}-3\right)\left(\sqrt{6}-2\right)}{2}\)

\(=\dfrac{-3\left(2\sqrt{3}-2\sqrt{2}-3\sqrt{2}+2\sqrt{3}-6\sqrt{3}+6\right)}{2}\)

\(=\dfrac{-3\left(-2\sqrt{3}-5\sqrt{2}+6\right)}{2}\)

1, The homework is too difficult for him to do

2, The homework isn't easy enough for him to do

3, The homework is so difficult that he can't do it

4, It is such difficult homework that he can't do it

1. My sister says she went to school by bus this morning.

    My sister said she had gone to school by bus that morning.

2. Nga says she have done her homework.

    Nga said she had done her homework.

1, My sister says that she goes to school by bus this morning

My sister said that she had gone to school by bus this morning

2, Nga says that she have done her homework

Nga said that she had done her homework

1. He says his family are going to Da Nang this summer.

    He said his family were going to Da Nang that summer.

2. Anna says her mother wants to buy an electric bike for her.

     Anna said her mother wanted to buy an electric bike for her.

55470 : 86 = 645

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12. In spite of feeling tired, the man tried to finish the work.   

13.She swims very well.