1.We often made mistake last year.

      We used to made mistake last year

2. He began to work in this factory 3 years ago.

     He has begun to work in this factory for 3 years

3.This coat isn’t warm. I don’t wear it in winter.

This coat isn't warm enough to wear it in winter

4.She is beautiful and intelligent. She can become Miss World.

She is beautiful and intelligent enough to  become Miss World.

5. My brother usually got up late when she was young.

 My brother used get up late when he was young

7. Playing this game is very dangerous.

It’s dangerous to play this game .

8. It is good for you to revise five new words every day.

 You should revise five new words every day

9. Minh really loves to hang out with friends.

Minh really enjoys hanging out with friends

10. He doesn’t like getting up early on cold days.

-> He hates getting up early on cold days 

a) 4x + 12x² = 4x(1+ 3x)

b) x³ - 8 + 3x² - 6 = x³ +3x² -14

c) x² -2x +1 -4y² = (x-1)² -4y²

Câu 2:

a) x² + 5x - 3x - 15 = 0

⇔ x² + 2x +1 - 1 - 15 = 0

⇔ ( x+1)² =16

⇔ x + 1 =4

⇔ x = 3

b) 

a) ĐKXĐ: x≠ \(\dfrac{1}{2}\); x≠ \(\dfrac{-1}{2}\); x≠0

    A= \(\left(\dfrac{1}{2x-1}+\dfrac{3}{1-4x^2}-\dfrac{2}{2x+1}\right):\dfrac{x^2}{2x^2+x}\)

       = \(\left(\dfrac{2x+1-3-2\left(2x-1\right)}{4x^2-1}\right):\dfrac{x^2}{2x^2+x}\)

       =  \(\left(\dfrac{2x+1-3-4x+2}{4x^2-1}\right):\dfrac{x^2}{2x^2+x}\)

       = \(\dfrac{-4x}{\left(2x+1\right)\left(2x-1\right)}.\dfrac{x\left(2x+1\right)}{x^2}\)

       =  \(\dfrac{-4x^2}{x^2\left(2x-1\right)}\)

       = \(\dfrac{-4}{2x-1}\)

b) Tại x= -2 ta có A= \(\dfrac{-4}{2.\left(-2\right)-1}\)= \(\dfrac{4}{5}\)

c)  A= 4 ta có \(\dfrac{-4}{2x-1}\)=4

                  ⇔ -4 = 4(2x-1)

                  ⇔ -4 = 8x-4 

                   ⇔ x = 0

d)  A=1 ta có \(\dfrac{-4}{2x-1}\)=1

                   ⇔  -4 = 2x-1

                    ⇔ x= \(\dfrac{-3}{2}\)

Câu 1: Xác định nhanh hóa trị của mỗi nguyên tố hoặc nhóm nguyên tử trong các hợp chất sau đây:

NO: N=2, O=2        NO₂: N=4, O=2      N₂O₃: N=3, O=2      N₂O₅: N=5, O=2; NH₃: N=3, H=1       HCl: H=1, Cl=1       H₂SO₄: H=1, SO₄=2

H₃PO₄: H=1, PO₄=3      Ba(OH)₂: Ba=2, OH=1         Na₂SO₄: Na=1, SO₄=2;

NaNO₃: Na=1, NO₃=1        K₂CO₃: K=1, CO₃=2          K₃PO₄: K=1, PO₄=3         Ca(HCO₃)₂: Ca=2, HCO₃=1             Na₂HPO₄: Na=1, HPO₄=2

 Al(HSO₄)₃: Al=3, HSO₄=1         Mg(H₂PO₄)₂: Mg=2, H₂PO₄=1

Câu 2: Lập nhanh CTHH của những hợp chất sau tao bởi:

a/ S (VI) và O:  S+    O₂ →  SO₂     

 b/  P (V) và O:    4P+   5O₂→  2P₂O₅              

c/  C (IV) và H:     C+  2H₂→ CH₄                

d/  Fe (II) và O:    2Fe+  O₂→  2FeO

e/ Na (I) và OH (I):  Na+ OH→ NaOH

 f/ Cu (II) và NO₃(I): Cu+ NO₃→ Cu(NO₃)₂       

g/ Al (III) và SO₄ (II):  Al+ SO₄→ Al₂(SO₄)₃     

h/ NH₄ (I) và PO₄ (III): NH₄+ PO₄→ (NH₄)₃PO₄

Câu 3: Hãy sửa lại cho đúng các công thức hoá học sai trong các công thức hoá học sau:      

 AlCl₄ => AlCl₃            CuOH => Cu(OH)₂         Na(OH)₂ => NaOH

Ba₂O => BaO               Zn₂(SO₄)₃ => ZnSO₄          CaNO₃ => Ca(NO₃)₂

A

a)    2x²y(x²+xy-3y²)

= 2x⁴y + 2x³y² - 6x²y³

b)    (2x+1)(x-1)

= 2x²   -  2x  +  x -1

= 2x² -x -1

c)    (3xy²+6x²y-9xy):3xy

=  y + 2x - 3

d)   \(\dfrac{2x+7}{x+1}+\dfrac{x-4}{x+1}\)

= \(\dfrac{2x+7+x-4}{x+1}\)

= \(\dfrac{3x+3}{x+1}\)

= \(\dfrac{3\left(x+1\right)}{x+1}\)= 3

e)  \(\dfrac{\left(x+2\right)^2}{x-1}:\dfrac{x+2}{3x-3}\)

= \(\dfrac{\left(x+2\right)^2}{x-1}.\dfrac{3\left(x-1\right)}{x+2}\)

= 3(x+2) = 3x+6

f)  \(\left(\dfrac{x^2+2x+2}{x+2}-\dfrac{1}{x+2}\right):\dfrac{x-1}{x+2}\)

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

= \(\dfrac{x^2+2x+1}{x+2}.\dfrac{x+2}{x-1}\)

= \(\dfrac{\left(x+1\right)^2}{x-1}\)

\(\dfrac{1}{\sqrt{5}}-\sqrt{3}-\dfrac{1}{\sqrt{5}}+\sqrt{3}\)

= \(\dfrac{1}{\sqrt{5}}-\dfrac{1}{\sqrt{5}}-\sqrt{3}+\sqrt{3}\)

=0

the boy always spends much time playing game.

^{1.a    2.c    3.b    4.b   5,b}

1/ The ( science )......................can know when a volcano will erupt.

=> scientists

2/ The village was ( complete )....................................................destroyed by the typhoon last week.

=> Completly

3/ Many people become (home ).........because of the (nature).........................disasters every year.

=> homless- nation

4/ ( Tidal ) ...............................waves are the result of an abrupt shift in the underwater movement of the earth.

=> tidal

5/ He was very tired, so he walked ( slow )..............

=> slowly

6/ If we go on littering, our environment (become).....................................................seriously polluted.

=> will become

7/ Tet is the most ( importance )............................................festival  for Vietnamese people.

=> important

8/  Do you know the reason for ( celebrate )..........................Mother’s day?

=> celebrating

9/ We are very ( pride )....................................................of our fatherland.

=> proud

10/ They take part in many ( culture )..................................activities in their town.

=> cultural

11/ Easter is a ( joy ).............festival which is ( celebrate ).....................in many nations.

=> joyful - celebrated

12/ Everybody cleans and ( decoration )...........................the houses for Tet.

=> decorates

13/ She is always ( worry )............................................about her children because she lives far from them.

=> worried

14/ He is an ( active )............................in the town charity program. He is very ( active )................................

=> activist- active

15/ Pompeii was completely destroyed in AD. 79 by an ( erupt ).......................................of Mount Vesuvius.

=> eruption

16/ We can reduce garbage by ( recycle )......................................waste things.

=> recycle

17/ He ( learn ).....................................English since he was ten years old.

=> has learnt

18/ My teacher suggests ( put )....................................garbage bins around the schoolyard.

=> putting

19/ If you can’t find your place, he ( help )..................................you to get there with this map.

=> will help

20/ What might happen if the ( pollute )........................................goes on?.

=>pollution

They live ( happy ).......................................although they are very rich.

=> happiness