Ta có: x = a.3 - 2 mà a = {0 ; 1 ; 3 ; 5} nên ta được:

TH₁ : a = 0  => x = 0.3 - 3  => x = -3 (loại)                                   TH₂ : a = 1  => x = 1.3 - 2  => x = 1 (chọn)

TH₃ : a = 3  => x = 3.3 - 2  => x = 7  (chọn)                                   TH₄ : a = 5  => x = 5.3 - 2  => x = 13 (chọn)

Vậy C = { 1 ; 7 ; 13}

(7x-3)(2x+1)-(5x-2)(x+4)-9x²+17x

(6x-5)(x+8)-(3x-1)(2x+3)-9(4x-3)

-3x(x+2)²+(x+3 )(x-1)(x+1)-(2x-3)²

^{rút gọn}

Bài 1 rút gọn các biểu thức sau

a)(6x+1)mũ 2 +(6x-1)mũ 2 -2(1+6x)(6x-1)

b)3x(x-2)-5x(1-x)-5(x mũ 2 -3)

Bài 3 choose the correct options to fill in the blanks

In Western countries , people use knives and forks during meals . (1)...........eating western - style food , a knife should be held in the right hand (2)......... a fork should be held in left hand . (3) ....., the different ways knives and forks place have different meanings . For example , you have to leave (4) ..... a while when you have a meal , you can put the knife and fork (5) .....as a triangle . If you have already finished the meal , you should make the knife and fork paralleled . Bread is taken in th fingers and (6)......,on the side of plate or the edge of the large plate . It is never taken

3 Do you get used to using chopsticks

Are you familiar

4 You don't have to wear uniform

It is not necessary

Bai 2 Rewite the sentences

1 Children should take things from adults with both hands

Children had

2 We decorate our house with a lot of flowers a Tet

Our house

6 When / visit / someone's house / do / not / forget / bring / present

7 Vietnamese / people / usually / spend / weekends / have / meals / together

8 Remember / ask / for / parents / permission /before / go / out / friends

Viết lại câu

1 Japanese / customs / different / Vietnamese / ones

2 Our / house / have to / clean / carefully / when / tet / come

3 Parents / often / want / children / follow / family / traditions

4 Hung / talk / Peter / one / his /family / traditions / at present

5 You / should / not / wear / shorts / when / visit / temple