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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

1: \(2155-\left(174+2155\right)+\left(-68+174\right)\)

=2155-174-2155-68+174

=(2155-2155)+(174-174)-68

=-68

2: \(-25\cdot72+25\cdot21-49\cdot25\)

\(=25\left(-72+21-49\right)\)

\(=25\cdot\left(-100\right)=-2500\)

3: \(35\left(14-23\right)-23\left(14-35\right)\)

\(=35\cdot14-35\cdot23-23\cdot14+23\cdot35\)

\(=35\cdot14-23\cdot14=12\cdot14=168\)

4: \(8154-\left(674+8154\right)+\left(-98+674\right)\)

=8154-674-8154-98+674

=(8154-8154)+(674-674)-98

=0+0-98

=-98

5: \(-25\cdot21+25\cdot72+49\cdot25\)

\(=25\left(-21+72+49\right)\)

\(=25\cdot100=2500\)

6: \(27\left(13-16\right)-16\left(13-27\right)\)

\(=27\cdot13-27\cdot16-16\cdot13+16\cdot27\)

\(=27\cdot13-16\cdot13=11\cdot13=143\)

7: -1911-(1234-1911)

=-1911-1234+1911

=-1234

8: \(156\cdot72+28\cdot156\)

\(=156\cdot\left(72+28\right)\)

\(=156\cdot100=15600\)

9: \(32\cdot\left(-39\right)+16\cdot\left(-22\right)\)

\(=16\cdot\left(-78\right)+16\cdot\left(-22\right)\)

\(=16\cdot\left(-78-22\right)=16\cdot\left(-100\right)=-1600\)

10: -1945-(567-1945)

=-1945-567+1945

=-567

11: \(184\cdot33+67\cdot184\)

\(=184\cdot\left(33+67\right)\)

\(=184\cdot100=18400\)

12: \(44\cdot\left(-36\right)+22\cdot\left(-28\right)\)

\(=22\cdot\left(-72\right)+22\cdot\left(-28\right)\)

\(=22\cdot\left(-72-28\right)=22\cdot\left(-100\right)=-2200\)

B C C A  B D C

1 B

2 C

3 C

4 A

5 B

6 D

7 C

Does your father get to work by bicycle?

Does your father get to work by bicycle?

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 

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

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

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

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

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

Sửa lại pt : \(FeCl_2+H_2SO_4\rightarrow FeSO_4+2HCl\)

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

cảm ơn :3

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

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

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