David asked the doctor why he often slept in class although he tried hard to break his bad habit.

1. D: Peter Pan who was my classmate will visit my aunt this Sunday.

N: Peter Pan, who was my classmate, will visit my aunt this Sunday.

2. D: Kenny who is the lovely boy is in my class.

N: Kenny, who is the lovely boy, is in my class.

3. D: Mary is arguing with Peggy who is a horrible person.

Mary is arguing with Peggy, who is a horrible person.

4. D: I will go shopping with Anna who is a hardworking person.

N: I will go shopping with Anna, who is a hardworking person.

Vì `x^2  >=0\ forall x -> x^2+1 >= 1 >0 `

` -> 3-x=0`

`-> x=3`.

28. D -> problems yet.

29. B -> hadn't gone

30. D -> following day

C.

a) `(4x^4y-7x^2y+3y).(2y-3x^2y)`

`=8x^4y^2-14x^2y^2+6y^2-12x^6y^2+21x^4y^2-9x^2y^2`

`=29x^4y^2-12x^6y^2-23x^2y^2+6y^2`

b) `(x^2+3x-3/2 x^3):2x - x/2 . (1-3/2 x)`

`=(x+3-3/2 x^2):2 - (x/2 - 3/4 x^2)`

`=x/2 + 3/2 - 3/4 x^2 -x/2 +3/4 x^2`

`=3/2`

c) `(-2x^3-x-3+5x^2):(3-2x)`

`=(3-2x)(x^2-x-1) : (3-2x)`

`=x^2-x-1`

Sai môn rồi bạn.

`1/125 x^3 -1 = (1/5 x)^3 -1^3=(1/5 x-1)(1/25 x^2 +1/5 x +1)`