1. had already prepared (một hành động xảy ra trc một hành động khác trong quá khứ với dấu hiệu already trong câu => dùng thì QKHT)

2. will have lived (By the time: dấu hiệu của thì TLHT)

3. encourages (HTĐ)

4. will have (TLĐ)

5. is shopping (HTTD) - will be (TLĐ)

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

13.She swims very well.

have played

Were - was

enjoys collecting - has had

goes - has been

is said to be

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

is a big supermarket next to our school

not met him for 3 months

10-day Tet holiday

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:

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

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

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

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

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

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

representatives

natural - include

recycling

mixture

environmentally

packaging