B là đúng nhất hjhj

267

la  3 hoac 5

a) A={0 ; 1 ; 2 ; 3 ; 4 ; 5 ; 6 ; 7 ; 8 ; 9}

b) Tập hợp A có 10 phần tử

c) 7 ∈ A

{ 7 } ⊂ A

Choose the word (A, B, C or D) that best fits the blank space in the following passage.

One of the (13) _______ things that can happen on our earth is an earthquake. When earthquakes take place near large cities, many people may be killed and many buildings are (14) _______ down. Fire may start and (15) _______ more damage than the quake itself. Earthquake comes (16) ______ a shaking of the rocks under the surface of the earth. Forces within the earth push against the rocks until they break. We cannot tell exactly (17) _______ an earthquake is coming, but we can know places on the (18) _______ where they happen most often.

Điền vào số 18

A. world

B. country

C. earth

D. reason

Khó quá do thi phuong nhung

Câu 1 : ?

Câu 2 : 280

tick bn nha

Vì a + 5b ⋮ 7 ⇒ 4 . (a + 5b) ⋮ 7 ⇒ 4a + 20b ⋮ 7)

Xét tổng :

(4a + 20b) + (10a + b)

= 4a + 20b + 10a + b

= (4a + 10a) + (20b + b)

= 14a + 21b

= (2a + 3b) . 7 ⋮ 7

⇒ (4a + 20b) + (10a + b) ⋮ 7 (1)

Mà 4a + 20b ⋮ 7 (2)

Từ (1) và (2) ⇒ 10a + b ⋮ 7 (đpcm)

Vậy 10a + b ⋮ 7