Hi Phuong, 

How is everything going on ? Thanks for your last email. Now I'll tell you about my house.

I live in a town house with my grandfather, my paerents, my elder sister and my younger sister. My house is on Cau Giay Street. It is really big. There are siveven room: a living room, three bedroom, two bathroom and a kitchen. My bedroom is next to the bathroom. There is a bed, a bookcase and two lamps in my bedroom. One of the lamps is on the desk next to the bed. The other lamp is near the bookcase. I really love my bedroom so I decorate it with a lotg of posters and coins that I have collected.

How about you? Write me soon and tell me about your house\

Best regards,

Lan

Dear..,

Thanks for your letter. Now, I'm speaking for you about my home.

My home has ... room: (The room themselves). .. (You name the room, location and characteriss, which can be added to what is in that room).

Write to me soon,
Love!

(Your name)

 Đặt cột s+s theo từng cặp số hạng (số đầu-số đuôi) nhé: 
s = 1 + 2 + 3 +...+ 999 
+ 
s = 999 + 998 + 997 +...+ 1 
__________________________ 
2s=1000+1000+1000+...+1000 

2s=1000.999 (từ 1 đến 999 <=> có 999 số hạng) 
=> s= 500.999= 499500

a) 1 + 2 + 3 + ... + 999

số số hạng là: 999-1+1=999(số hạng)

tổng là:(999+1).999:2=499500

Mình nghĩ là bằng 309

152 . 75 + ( 152 + 4 ) .25 = ( 152 . 3 ) . 25 +  ( 152 + 4 ) .25

                                     = 456 . 25 + 156 . 25 

                                     = 25 . ( 456 + 156 ) 

                                     = 25 . 612

                                     = 15300

a) 0 : x = 0

=> x \(\in\)N ( x \(\ne\)0 )

b) 3^x = 9

=> x = 2

c) 4^x = 64

=> x = 3

d) 2^x = 16 

=> x = 4

e) 9^x-1 = 9

9 = 9¹ 

=> x = 1 + 1 = 2

x⁴ = 16

=> x = 2

g) 2^x : 2⁵ = 1

Quy ước a⁰ = 1 , ta suy ra : x = 5

Giải ko giải thích , bỏ qua nhá :))

Mình chưa có học lớp 6 nên mk ko biết.Sorry nha

\(5x+2x=6^2-5^0\Leftrightarrow5x+2x=6^2-1\)

\(\Leftrightarrow5x-2x=36-1\Leftrightarrow5x-2x=35\Leftrightarrow x\left(5+2\right)=35\)

\(\Leftrightarrow7x=35\Leftrightarrow x=35:7\Leftrightarrow x=5\)

\(5x+x=150:2+3\Leftrightarrow5x+x=75+3\)

\(\Leftrightarrow5x+x=78\Leftrightarrow x\left(5+1\right)=78\Leftrightarrow x6=78\)

\(\Leftrightarrow x=78:6\Leftrightarrow x=13\)

a) 5x + 2x = 6² - 5⁰

7x = 35 => x = 5

b) 5x + x = 150 : 2 + 3

6x = 78 => x = 13

c) 6x + x = 5¹¹ : 5⁹ + 3¹

7x = 28 => x = 4

d) 5x + 3x = 3⁶ : 3³ x 4 + 12

8x = 120 => x = 15

e) 4x + 2x = 68 - 2¹⁹ : 2¹⁶

6x = 60 => x = 10

f) 5x + x = 39 - 3¹¹ : 3⁹

6x = 30 => x = 5

g) 7x - x = 5²¹ : 5¹⁹ + 3 x 2² - 7⁰ 

6x = 36 => x = 6

h) 7x - 2x = 6¹⁷ : 6¹⁵ + 44 : 11

5x = 40 => x = 8

gọi d là ƯC(8a+3 ;5a+2)

Ta có:8a+3 chia hết cho d ; 5a+2 chia hết cho d

Nên 8a+3-5a+2

=> 2(8a+3)-3(5a+2) chia hết cho d

 => 1 chia hết cho d

Vậy d=1 nên 8a+3 và 5a+2 là hai số nguyên tố cùng nhau

Gọi d là ƯC_{(8a + 3; 5a + 2)} 

Ta có 8a + 3 \(⋮\)d; 5a + 2 \(⋮\)d

Nên (8a + 3) - (5a + 2)

=> 2.(8a + 3) - 3.(5a + 2) \(⋮\)d 

= 1 \(⋮\)d => d = 1

Vì d = 1 => 8a + 5 và 5a + 2 là hai số nguyên tố cùng nhau.

ta có :

 a - 1 \(\in\) BC( 2 , 3 , 4 , 5 , 6 ) \(\Rightarrow\) a - 1 \(\in\) { 60 , 120 , 180 , 240 , 300 , 360 }

Do a \(⋮\) 7 nên a = 301

                 vậy , ta tìm được a = 301

Tham khảo nhé:

To: cococococococococo@yahoo.com

Subject: My house

Hi Phong,

Thanks for your e-mail. Now I'll tell you about my house. I live with my parents and my brother in a city house. It's not so big but it's very comfortable. There are five rooms: a living room, a kitchen, a bedroom, a bathroom and hall. I my bedroom best. What about you? Where do you live? Tell me in your next e-mail.

Best wishes,

Duc

Hi...., my name is.....
How are you? I'm very happy now. Are you happy now? Now I will tell you about your beautiful house. Outside the house is the flower garden and old trees are old.The house has a washing machine, refrigerator and robots, and they are wonderful! And next, I will tell you about your friends line, they are very funny!! So I love this life very much. Goodbye and see you in the next letter offline!

a) x*(1+2+3+...+20)=2100

                   x*210 =2100

                   x        =10

dấu * là nhân hả bạn

\(8x+2x=25\cdot2^2\Leftrightarrow8x+2x=25\cdot4\)

\(\Leftrightarrow8x+2x=100\Leftrightarrow x\left(8+2\right)=100\)

\(\Leftrightarrow x\cdot10=100\Leftrightarrow\orbr{\begin{cases}x=100:10\\x\cdot10=10\cdot10\end{cases}}\)

\(\Leftrightarrow x=10\)

Vậy giá trị x cần tìm để thỏa mãn yêu cầu của đề bài là \(x=10\)

8x + 2x = 25 . 4

10x = 100

=> x = 100 : 10 = 10