I

1 D

2 C

3 B

4 A

5 B

II

1 How does Mr. Hai travel to work?

2 What do they often do in the summer?

3 What does your mother need ?

4 Where does Jane's sister works?

5 When do these students have English?

III

1 is singing

2 watches

3 Did - work

5 won't eat

6 speak

IV

1 buying => to buy

2 goes shopping always => always goes shopping

3 in => for

4 breads => bread

5 the => of the

V

1 river

2 afternoon

3 work

4 fishes

5 There

6 people

7 too

8 hours

9 sometimes

10 because

VI

1 My sister often goes to the supermarket on foot

2 Are there 50 students in your class?

Bài 4 : 

\(M=\left(2x-3y\right)^2-\left(3y-2\right)\left(3y+2\right)-\left(1-2x\right)^2+4x\left(3y-1\right)\)

\(=\left(2x-3y-1+2x\right)\left(2x-3y+1-2x\right)-9y^2+4+12xy-4x\)

\(=\left(4x-3y-1\right)\left(1-3y\right)-9y^2+4+12xy-4x\)

\(=4x-12xy-3y+9y^2-1+3y-9y^2+4+12xy-4x=3\)

Vậy biểu thức ko phụ thuộc giá trị biến x 

Bài 2 : 

a, \(\left(a-3b\right)^2=a^2-6ab+9b^2\)

b, \(x^2-16y^4=\left(x-4y^2\right)\left(x+4y^2\right)\)

c, \(25a^2-\frac{1}{4}b^2=\left(5a-\frac{1}{2}b\right)\left(5a+\frac{1}{2}b\right)\)

Bài 3 : 

a, \(9x^2-6x+1=\left(3x-1\right)^2\)

b, \(\left(2x+3y\right)^2+2\left(2x+3y\right)+1=\left(2x+3y+1\right)^2\)

c, \(4\left(2x-y\right)^2-8x+4y+1=\left(4x-2y\right)^2-2\left(4x-2y\right)+1=\left(4x-2y-1\right)^2\)

Bài 5 : 

a, \(E=x^2-8x+38=x^2-8x+16+22=\left(x-4\right)^2+22\ge22\)

Dấu ''='' xảy ra khi x = 4

Vậy GTNN của E bằng 22 tại x = 4

b, \(F=-x^2+6x+1=-\left(x^2-6x+9-9\right)+1=-\left(x-3\right)^2+10\le10\)

Dấu ''='' xảy ra khi x = 3

Vậy GTLN của F bằng 10 tại x = 3

4.2:

a: x^2-x+1=x^2-x+1/4+3/4

=(x-1/2)^2+3/4>=3/4>0 với mọi x

=>x^2-x+1 ko có nghiệm

b: 3x-x^2-4

=-(x^2-3x+4)

=-(x^2-3x+9/4+7/4)

=-(x-3/2)^2-7/4<=-7/4<0 với mọi x

=>3x-x^2-4 ko có nghiệm

5:

a: x^2+y^2=25

x^2-y^2=7

=>x^2=(25+7)/2=16 và y^2=16-7=9

x^4+y^4=(x^2)^2+(y^2)^2

=16^2+9^2

=256+81

=337

b: x^2+y^2=(x+y)^2-2xy

=1^2-2*(-6)

=1+12=13

x^3+y^3=(x+y)^3-3xy(x+y)

=1^3-3*1*(-6)

=1+18=19

1 disastrious

2 harmless 

3 enrich 

4 informal 

5 musician

1. diastrious

2. harmless

3. enrich

4. informal

5. musician

1 correct

2 incorrect

3 incorrect

4 correct

5 incorrect

6 correct

7 correct

8 incorrect

9 incorrect

10 correct

`bb8)`

`( x-2/3)(10-2x) = 0`

`<=> x-2/3=0` hoặc `10-2x=0`

`<=> x = 2/3` hoặc `2x=10`

`<=> x=2/3` hoặc `x=5`

Vậy `S={2/3;5}`

`bb9)`

`( x + 9 )( x-3 )( x + 21 )=0`

`<=> x+9=0` hoặc `x-3=0` hoặc `x+21=0`

`<=> x=-9` hoặc `x=3` hoặc `x=-21`

Vậy `S={-9;3;-21}`