Thay `b=5a+2c` vào `ax^2+bx+c=0`:

`ax^2+(5a+2c)x+c=0`

`=>Delta=(5a+2c)^2-4ac`

`=25a^2+20ac+4c^2-4ac`

`=25a^2+16ac+4c^2`

`=9a^2+(16a^2+16ac+4c^2)`

`=9a^2+(4a+2c)^2>=0`

`=>` ĐPCM

mountains

Choose the best answer:
1.___do you go shopping? –Once a week.
(How/ Why/How often/ How far)
2.__is it from your school to house?-About 1km
(How much/How far/ When/Where)
3.Yesterday she bought meat,fish___vegetables.
(and/ but/ or/ so)
4.She is thin,___she is strong.
(but/ although/ or/ if)
5.Odd one out:
(boat/town/ house/crowded)
6.Odd one out:
(earth/ anything/through/than)
7.Odd one out:
(there/ them/both/neither)
8.Yesterday, she (play/played/plays/ is playing)
the piano.
9.Hoa:What___you do last night?
(was/were/did/ does)
Nam: I watched T.V.
10.A:Where (is/ are/ was/were)__you last year?
B: I was at Cua Lo beach.
11.Tìm từ trái nghĩa: quiet ><___
(boring/ interesting/ modern/ traditional/noisy)
12.Sửa lỗi sai:
We are interested of watching cartoons.
 A                B       C                       D
13.Not go out at night.  
       A    B  C  D
14.This car belongs to my father.It is___
                     thuộc về        (her/him/his/ mine)
15.I have a cat. The cat is ____. (my/mine/I/me)
16.Odd one out:
(arrived/ moved/ laughed/ enjoyed)
17.Odd one out:
(invited/ decided/ prepared/ wanted)
 18.Dung loves sports.He is so (sporty/ sports)
19.Ha has a gift. The gift belongs to (Ha/Ha’s)
20.When you ride a motorbike.You should wear a( hat/ boot/ helmet/ jacket) to protect 

`a/(x+1)+b/(x-2)=(a(x-2)+b(x+1))/((x+1)(x-2))`

`=(ax-2a+bx+b)/(x^2-x-2)`

`=((a+b)x+(-2a+b))/(x^2-x-2)`

``

Theo đề bài: `((a+b)x+(-2a+b))/(x^2-x-2)=(32x-19)/(x^2-x-2)`

Đồng nhất hệ số ta được: `{(a+b=32),(-2a+b=-19):}` 

`<=>{(a+b=32),(2a-b=19):}`

`<=>{(3a=51),(a+b=32):}`

`<=>{(a=17),(17+b=32):}`

`<=>{(a=17),(b=15):}` 

A.

AB=AE

AD=AC

A vuông

`=>` 2 tam giác bằng nhau

`=>` Đúng

``

B.

2 tam giác bằng nhau `=> BC=ED`

`=>` Đúng

``

D. Giống với A

`=>` Đúng

``

`=>` C sai

1. A.'tropical   B.di'saster   C.'damage   D.'chemical

2. A.pol'lution   B. contami'nation   C.des'troy   D.en'vironment

\(A\left(x\right)=2x^2-x^3\\ B\left(x\right)=x^3-2x^2+3x-1\)

``

a) `P(x)=A(x)+B(x)`

`=2x^2-x^3+x^3-2x^2+3x-1`

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

`=3x-1`

``

b) `P(x)=0`

`3x-1=0`

`3x=1`

`x=1/3`

Số cần tìm có dạng `3overline(ab)`

Tổng các chữ số là 12 `=> 3+a+b=12=>a+b=9`

Số đó nằm giữa 300 và 320 `=>a \in {0;1}`

TH1: `a=0 => b=9=>` Số đó là: 309

309 không chia hết cho 6

TH2: `a=1 => b=8 =>` Số đó là: 318

318 chia hết cho 6

Vậy Keria đang nghĩ đến số 318.

If I were you, I would go there alone.