`@` `\text {Ans}`

`\downarrow`

`18,`

`2^(3x+1) = 16`

`=> 2^(3x + 1) = 2^4`

`=> 3x+1 = 4`

`=> 3x = 4 - 1`

`=> 3x = 3`

`=> x = 1`

Vậy, `x = 1`

`=> A`

`19,`

`9^12 * 27^5`

`= (3^2)^12 * (3^3)^5`

`= 3^24 * 3^15`

`=3^39`

`=> D`

`20,`

`100 < 5^(2x - 1) < 5^5`

`=> 2x - 1 < 5`

`=> x < 3 => x \in {0; 1; 2}`

`=> D`

`21,`

`5^x < 90`

`=> x < 3`

`=> x \in {0; 1; 2}`

`=> B`

`22,`

`(7x - 11)^3 = 5^2 * 2^5 + 200`

`=> (7x - 11)^3 = 25 * 32 + 200`

`=> (7x - 11)^3 = 800 + 200`

`=> (7x - 11)^3 = 1000`

`=> (7x - 11)^3 = 10^3`

`=> 7x - 11 = 10`

`=> 7x = 21`

`=> x = 3`

`=> C`

`23,`

`(x - 4)^5 = (x - 4)^4`

`=> (x - 4)^5 - (x - 4)^4 = 0`

`=> (x - 4)^4 * (x - 4 - 1) = 0`

`=> \text {TH1:} (x - 4)^4 = 0`

`=> x - 4 = 0`

`=> x = 4`

`\text {TH2:} x - 4 - 1 = 0`

`=> x - 5 = 0`

`=> x = 5`

Tổng của `2` stn x thỏa mãn dk là: `4 + 5 = 9`

`=> A.`

36 D

37 B

38 C

39 C

40 D

41 D

42 A

43 D

44 D

45 A

46 D

47 B

48 C

49 D

50 D

51 B

52 C

53 B

54 C

55 C

56 C

57 B

58 A

59 C

60 B

61 B

62 C

63 C

64 C

13 D

14 A

15 A

16 C

17 B

18 A

19 C

20 B

1 the cleverest

2 longer

3 the best

4 cleaner

5 more expensive

6 the most quickly

7 more dangerous

8 more sweetly

9 the most exciting

10 the fastest

1 beautifully

2 carefully

3 badly

4 quietly

5 loud

6 happily

7 fast

8 well

9 terribly

10 early

11 hard

12 late

a: Thay x=-2 và y=8 vào (P), ta được:

\(8=2\cdot\left(-2\right)^2\)(đúng)

Vậy: A(-2;8) thuộc (P)

b: Câu này bạn chỉ cần lập bảng xong rồi vẽ thôi

a) Từ trái qua phải 

\(Na_2O+H_2O\rightarrow2NaOH\)

\(2NaOH+CO_2\rightarrow Na_2CO_3+H_2O\)

\(Na_2CO_3+H_2SO_4\rightarrow Na_2SO_4+CO_2\uparrow+H_2O\)

\(Na_2SO_4+BaCl_2\rightarrow2NaCl+BaSO_4\downarrow\)

b) Từ trái qua phải 

\(Fe+2HCl\rightarrow FeCl_2+H_2\uparrow\)

\(FeCl_2+2NaOH\rightarrow Fe\left(OH\right)_2\downarrow+2NaCl\)

\(Fe\left(OH\right)_2\xrightarrow[]{t^o}FeO+H_2O\)

\(FeO+2HCl\rightarrow FeCl_2+H_2O\)

\(2FeCl_2+4H_2SO_{4\left(đ,n\right)}\rightarrow Fe_2\left(SO_4\right)_3+4HCl+SO_2\uparrow+2H_2O\)

Bài 2: 

a: 3/8=81/216

5/27=40/216

b: -2/9=-50/225

4/25=36/225

c: 1/15=1/15

-6=-90/15

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

\(\Leftrightarrow\left\{{}\begin{matrix}\left(-8-2\sqrt{5}\right)y=6\sqrt{5}+2\\2x-3y=3\sqrt{5}-1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=1-\sqrt{5}\\x=\dfrac{3\sqrt{2}-3\sqrt{5}+2}{2}\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}4x-6y=6\sqrt{5}-2\\3.\left(\sqrt{5}-1\right)x+6y=3-3\sqrt{5}\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}\left(3\sqrt{5}+1\right)x=1+3\sqrt{5}\\y=\dfrac{3\sqrt{5}-1-2x}{-3}\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}x=1\\y=\dfrac{3\sqrt{5}-1-2.1}{-3}\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}x=1\\y=\dfrac{-3.\left(1-\sqrt{5}\right)}{-3}=1-\sqrt{5}\end{matrix}\right.\\ \Rightarrow\left(x;y\right)=\left(1;1-\sqrt{5}\right)\)