1. \(\sqrt{1-12x+36x^2}=5\)

ĐKXD: \(1-12x+36x^2\ge0\Leftrightarrow\forall x\in R\)

\(\Leftrightarrow\sqrt{\left(6x\right)^2-2.6x.1+1^2}=5\)

\(\Leftrightarrow\sqrt{\left(6x-1\right)^2}=5\)

\(\Leftrightarrow\left|6x-1\right|=5\)

\(\Leftrightarrow\left[{}\begin{matrix}6x-1=5\\6x-1=-5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}6x=6\\6x=-4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-\dfrac{2}{3}\end{matrix}\right.\)

2. \(\sqrt{1-4x+4x^2}=5\)

ĐKXD: \(1-4x+4x^2\ge0\Leftrightarrow\forall x\in R\)

\(\Leftrightarrow\sqrt{\left(2x\right)^2-2.2x.1+1^2}=5\)

\(\Leftrightarrow\sqrt{\left(2x-1\right)^2}=5\)

\(\Leftrightarrow\left|2x-1\right|=5\)

\(\Leftrightarrow\left[{}\begin{matrix}2x-1=5\\2x-1=-5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x=6\\2x=-4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=-2\end{matrix}\right.\)

4.  \(\sqrt{x^2+6x+9}=x-1\)

ĐKXD: \(x^2+6x+9\ge0\Leftrightarrow\forall x\in R\)

\(\Leftrightarrow\sqrt{\left(x+3\right)^2}=x-1\)

\(\Leftrightarrow\left|x+3\right|=x-1\)

\(\Leftrightarrow\left[{}\begin{matrix}x+3=x-1\\x+3=-x+1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}0x=-4\\2x=-2\end{matrix}\right.\Leftrightarrow x=-1\)

5, \(\sqrt{x^2+x+\dfrac{1}{4}}=x\)

ĐKXD: \(x^2+x+\dfrac{1}{4}\ge0\Leftrightarrow\forall x\in R\)

\(\Leftrightarrow\sqrt{\left(x+\dfrac{1}{2}\right)^2}=x\)

\(\Leftrightarrow\left|x+\dfrac{1}{2}\right|=x\)

\(\Leftrightarrow\left[{}\begin{matrix}x+\dfrac{1}{2}=x\\x+\dfrac{1}{2}=-x\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}0x=-\dfrac{1}{2}\\2x=-\dfrac{1}{2}\end{matrix}\right.\Leftrightarrow x=-\dfrac{1}{4}\)

Câu 3 thiếu đề nhé.

1. I enjoy telling jokes.

2. Our characters are quite different.

3. My family has four people.

26. a -> an

27. such -> so

28. are -> is

29. many -> much

30. getting -> to get

DKXD: \(x\ge4\)

\(\sqrt{x+4\sqrt{x-4}}=2\)

\(\Leftrightarrow\sqrt{\left(x-4\right)+2.\sqrt{x-4}.2+4}=2\)

\(\Leftrightarrow\sqrt{\left(\sqrt{x-4}+2\right)^2}=2\)

\(\Leftrightarrow\left|\sqrt{x-4}+2\right|=2\)

\(\Leftrightarrow\sqrt{x-4}+2=2\)

\(\Leftrightarrow\sqrt{x-4}=0\)

\(\Leftrightarrow x-4=0\)

\(\Leftrightarrow x=4\)

2. little

3. any

4. many

5. a few

6. little

7. some

8. some

9. few

10. little

11. any

12. some

13. any

14. any - some

15. some

1, My class has 18 tables.

2, There are 5 windows in my class.

3, My school has 16 classrooms.

4, Huy is taller than Hung.

a, 2k+1, 2k+3, 2k+5

b, Ta có: \(\left(2k+3\right)\left(2k+5\right)-\left(2k+1\right)\left(2k+3\right)=20\)

\(\Leftrightarrow\left(2k+3\right)\left(2k+5-2k-1\right)=20\)

\(\Leftrightarrow\left(2k+3\right).4=20\)

\(\Leftrightarrow2k+3=5\)

\(\Leftrightarrow2k=2\)

\(\Leftrightarrow k=1\)

Vậy 3 số cần tìm là 3,5,7.

36c

37c

38a

39a

40b

41b

42b

43d

44a

45d

46d

47c

48b

49a

50b

1. C

2. A

3. B

4. B

5. A

1. B -> helped

2. A -> obedient

3. D -> happy

4. D -> hasn't finished

5. A. -> haven’t seen

6. C -> hurries

7. D -> taking care of

8. B ->mending

9. B -> to win 

10. B -> as