b b c a d

1 B

2 B

3 D

4 A

5 D

c: \(C=\left(x+y\right)^2-\left(x-y\right)^2\)

\(=\left(x+y+x-y\right)\left(x+y-x+y\right)\)

=4xy

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

Ex1:
1. might have
2. had to 
3. didn't have to
4. could
5. shouldn't have
6. couldn't have
Ex2:
1. don't have to
2. must
3. Do you have to /don't have to / must
4. do not need to / must

help

Ex1:

1, might have

2, had to

3, didn't have to

4, could

5, shouldn't have

6, couldn't have

Ex2:

1, don't have to 

2, must

3, Do you have to - don't have to - must

4, do not need to - must

19 C

20 A

21 A

22 B

23 C

24 A

25 C

26 B

27 B

28 B

29 A

30 D

31 C

32 B

27. has never been

28. created

29. However

30. disconnecting

31. through

32. has become

33. with

34. to explore

35. However

32. has become
33. with
34. to explore
35. However
36. prevent

Help

Bài 1:

1B

2D

3E

4C

5A

6G

7F

2) 

a) (3x+y)(9x²-3xy+y²)=27x³+y³

b) (2x-5)(4x²+10x+25)

c)(2a+3b)(4a²-6ab+9b²)

d)(5x-4y)(25x²+20xy+16y²)=125x³-64y³

3)

b a b a b

A

C

B

Ai giúp em vơi :(