in ko bt đúng ko:)

on nhé
vì tg thì in chỉ dùng cho tháng, năm, mùa
còn on dùng cho ngày trong tháng (như trên bài), ngyaf trong tuần,...

Because of being ill, Lan had to stay at home

In spite of working very hard, she is poor

Because she was sick, she had to relax

Although I had breakfast this morning, I felt hungry

1.Because Lan was ill , she had to stay at home => Because of ...Lan's illness, she had to stay at home

2.Althought she works very hard , she is poor => In spite of ...working very hard, she is poor

3.Because of her sickness , she had to relax => Because ...she was sick, she had to relax

4. Despite having breakfast this morning , I felt hungry => Although I had breakfast this morning, I felt hungry

a) Tứ giác `ABCD` có `hat{A} + hat{B} + hat{C} + hat{D} = 360^o`

Do chúng lần lượt tỉ lệ với `2;3;6;7`

`=> hat{A}/2 = hat{B}/3 = hat{C}/6 = hat{D}/7`

Áp dụng t/chất dãy tỉ số bằng nhau:

`=>  hat{A}/2 = hat{B}/3 = hat{C}/6 = hat{D}/7 = (hat{A} + hat{B} + hat{C} + hat{D})/(2+3+6+7) = (360^o)/18 = 20^o`

`-> {(hat{A} = 20^o . 2 = 40^o),(hat{B} = 20^o  3 = 60^o),(hat{C} = 20^o . 6 = 120^o),(hat{D} = 20^o . 7 = 140^o):}`

Vậy ...

a) Ta có: 

`84 = 2^2 . 3 . 7`

`108 = 2^2 . 3^3`

`=> UCLN(84;108) = 2^2 . 3 = 12`

`=> UC(84;108) = Ư(12) = {-12;-6;-4;-3;-2;-1;1;2;3;4;6;12}`

Do `35 vdots x; 105 vdots x`

`=> x in UC{35;105)`

Mà `105 vdots 35`

`=> x in Ư(35) = {1;5;7;35}`

Mà `x > 5 -> x in {7;35}`

Vậy ...

`b) x vdots 10; x vdots 15`

`=> x in BC(10;15)`

Ta có: 

`10 = 2 . 5`

`15 = 3.5`

`=> BCN``N(10;15) = 2.3.5 = 30`

`=> x in B(30) = {0;30;60;90;120;...}`

Mà `x < 100 -> x in {0;30;60;90}`

`2/(1xx2xx3) + 2/(2xx3xx4) + ... + 2/(8xx9xx10) `

Ta có: 

`2/(1xx2xx3) = 1/(1xx2) - 1/(2xx3) `

`2/(2xx3xx4) = 1/(2xx3) - 1/(3xx4) `

....

`2/(8xx9xx10) = 1/(8xx9) - 1/(9xx10) `

Nên: `2/(1xx2xx3) + 2/(2xx3xx4) + ... + 2/(8xx9xx10) `

`= 1/(1xx2) - 1/(2xx3) + 1/(2xx3) - 1/(3xx4) + ... +  1/(8xx9) - 1/(9xx10) `

`= 1/2 - 1/90`

`= 22/45`

Vậy ....

\(\dfrac{2}{1\times2\times3}+\dfrac{2}{2\times3\times4}+\dfrac{2}{3\times4\times5}+\dfrac{2}{4\times5\times6}+...+\dfrac{2}{8\times9\times10}\)

\(=\dfrac{1}{1\times2}-\dfrac{1}{2\times3}+\dfrac{1}{2\times3}-\dfrac{1}{3\times4}+\dfrac{1}{3\times4}-\dfrac{1}{4\times5}+\dfrac{1}{4\times5}-\dfrac{1}{5\times6}+...+\dfrac{1}{8\times9}-\dfrac{1}{9\times10}\)

\(=\dfrac{1}{1\times2}-\dfrac{1}{9\times10}\)

\(=\dfrac{1}{2}-\dfrac{1}{90}\)

\(=\dfrac{22}{45}\)

là số:14,28 phải hum

Lời giải:

a. $140=2^2.5.7$

$168=2^3.3.7$

$\Rightarrow ƯCLN(140, 168) = 2^2.7=28$

b. 

$525=3.5^2.7$

$375=3.5^3$

$\Rightarrow ƯCLN(525, 375)=3.5^2=75$

Gọi số thứ nhất và số thứ hai lần lượt là: a,b
Trung bình cộng = a+b/2 = 285
=> a+b = 570
Ta có: 1/2 a = 1/3 b
=> a/2 = b/3
Áp dụng dãy tỉ số bằng nhau ta có: a/2 = b/3 = a+b/2+3 = 570/5 = 114
=> a = 2 x 114 = 228
=> b = 3 x 114 = 342
Vậy số thứ 1 = 228
       số thứ 2 = 342

Chỗ 570 = 285 x 2

`Ư(16) = {-16;-8;-4;-2;-1;1;2;4;8;16}`

`Ư(24) = {-24;-12;-8;-6;-4;-3;-2;-1;1;2;3;4;6;8;12;24}`

`=> ƯC(16;24) = {-8;-4;-2;-1;1;2;4;8}`

`Ư(30) = {-30;-15;-10;-6;-5;-3-2;-1;1;2;3;5;6;10;15;30}`

`Ư(45) = {-45;-15;-9;-5;-3;-1;1;3;5;9;15;45}`

`=> ƯC(30;45) = {-15;-5;-3;-1;1;3;5;15}`