11.

Gọi chiều dài và chiều rộng của hình chữ nhật ban đầu là x và y (x>y;x>2;y>1)

Diện tích ban đầu: \(xy\)

Diện tích sau khi tăng mỗi cạnh thêm 1cm: \(\left(x+1\right)\left(y+1\right)\)

Diện tích sau khi giảm chiều dài đi 2 và rộng đi 1: \(\left(x-2\right)\left(y-1\right)\)

Theo bài ra ta có hệ:

\(\left\{{}\begin{matrix}\left(x+1\right)\left(y+1\right)=xy+13\\\left(x-2\right)\left(y-1\right)=xy-15\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x+y=12\\x+2y=17\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}x=7\\y=5\end{matrix}\right.\)

12.

Gọi chiều dài của mảnh đất ban đầu là 0<x<40 thì chiều rộng là \(40-x\)

Diện tích ban đầu: \(x\left(40-x\right)\)

Diện tích sau khi tăng chiều dài thêm 3 và chiều rộng thêm 5 là: \(\left(x+3\right)\left(45-x\right)\)

Theo bài ra ta có pt:

\(\left(x+3\right)\left(45-x\right)=x\left(40-x\right)+195\)

\(\Leftrightarrow2x=60\Rightarrow x=30\)

Vậy mảnh đất dài 30 rộng 10

13.

Gọi số dãy ghế là x và số ghế trong mỗi dãy là y

\(\Rightarrow xy=40\)

Sau khi kê thêm 1 dãy và mỗi dãy thêm 1 chỗ thì số ghế là: \(\left(x+1\right)\left(y+1\right)\)

Ta có hệ: 

\(\left\{{}\begin{matrix}xy=40\\\left(x+1\right)\left(y+1\right)=55\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}xy=40\\x+y=14\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}x=10\\y=4\end{matrix}\right.\) hoặc \(\left\{{}\begin{matrix}x=4\\y=10\end{matrix}\right.\)

Vậy ban đầu trong phòng họp có 4 dãy hoặc 10 dãy ghế

        = 12/11

Thanks bạn!

Bài 8:

a) Chọn B

b) Chọn B

Bài 12: 

a: Xét ΔABM và ΔACN có

AB=AC

\(\widehat{ABM}=\widehat{ACN}\)

BM=CN

Do đó: ΔABM=ΔACN

11.

\(=\frac{\sqrt{x}-3}{2-\sqrt{x}}+\frac{\sqrt{x}-2}{3+\sqrt{x}}+\frac{9-x}{(2-\sqrt{x})(\sqrt{x}+3)}\)

\(=\frac{(\sqrt{x}-3)(\sqrt{x}+3)}{(2-\sqrt{x})(\sqrt{x}+3)}+\frac{\sqrt{x}-2}{3+\sqrt{x}}+\frac{9-x}{(2-\sqrt{x})(\sqrt{x}+3)}\)

\(=\frac{x-9}{(2-\sqrt{x})(\sqrt{x}+3)}+\frac{\sqrt{x}-2}{3+\sqrt{x}}+\frac{9-x}{(2-\sqrt{x})(\sqrt{x}+3)}\)

\(=\frac{\sqrt{x}-2}{3+\sqrt{x}}\)

12.

\(=\frac{(3-\sqrt{x})(3\sqrt{x}-2)+(5\sqrt{x}+7)(3\sqrt{x}+4)}{(5\sqrt{x}+7)(3\sqrt{x}-2)}-\frac{42\sqrt{x}+34}{(5\sqrt{x}+7)(3\sqrt{x}-2)}\) 

\(=\frac{12x+52\sqrt{x}+22}{(5\sqrt{x}+7)(3\sqrt{x}-2)}-\frac{42\sqrt{x}+34}{(5\sqrt{x}+7)(3\sqrt{x}-2)}\)

\(=\frac{12x+10\sqrt{x}-12}{(5\sqrt{x}+7)(3\sqrt{x}-2)}=\frac{2(3\sqrt{x}-2)(2\sqrt{x}+3)}{(5\sqrt{x}+7)(3\sqrt{x}-2)}=\frac{2(2\sqrt{x}+3)}{5\sqrt{x}+7}\)

13.

\(=\frac{(\sqrt{x}+2)(2\sqrt{x}-3)+(3\sqrt{x}-4)(-\sqrt{x}+2)}{(-\sqrt{x}+2)(2\sqrt{x}-3)}+\frac{-7\sqrt{x}+10}{(-\sqrt{x}+2)(2\sqrt{x}-3)}\)

\(=\frac{-x+11\sqrt{x}-14}{(-\sqrt{x}+2)(2\sqrt{x}-3)}+\frac{-7\sqrt{x}+10}{(-\sqrt{x}+2)(2\sqrt{x}-3)}\)

\(=\frac{-x+4\sqrt{x}-4}{(-\sqrt{x}+2)(2\sqrt{x}-3)}=\frac{-(\sqrt{x}-2)^2}{-(\sqrt{x}-2)(2\sqrt{x}-3)}=\frac{\sqrt{x}-2}{2\sqrt{x}-3}\)

11 More information was given to us by her

12 All the workers of the plan were being instructed by the chief engineer

13 Tea can't be made with cold water

14Some of my book have been taken away 

15 The meeting will be held before May Day

16 The engine of the car has to be repaired 

17 The window was broken and some pictures are taken away by the boyss

18 A lot of money is spent on advertising everyday

19 A story is going to be told by teacher

20 A cake is being cut with a sharp knife by Mary

21 The woman with a red hat was looked at by the children

22 The victims have been provided with food and clothing

23 English is spoken in almost every corner of the world

24 This machine mustn't be used after 530 pm

25 After class, the chalk board is always erased by one of the students

11. She gave us more information. More information was given us. 12. The chief engineer was instructing all the workers of the plan. All the workers were being instructed of the plan by the chief engineer. 13. They can’t make tea with cold water. Tea can't be made with cold water. 14. Somebody has taken some of my books away. Some of my books has been taken away. 15. They will hold the meeting before May Day. The meeting will be held before May Day. 16. They have to repair the engine of the car. The engine of the car has to be repaired. 17. The boys broke the window and took away some pictures. The window was broken and some pictures were taken away by the boys. 18. People spend a lot of money on advertising every day. A lot of money is spent on advertising every day. 19. Teacher is going to tell a story. A story is going to be told by teacher. 20. Mary is cutting a cake with a sharp knife. A cake is being cut with a sharp knife by Mary. 21. The children looked at the woman with a red hat. The woman with a red hat was looked at by the children. 22. They have provided the victims with food and clothing. The victims have been provided with food and clothing. 23. People speak English in almost every corner of the world. English is spoken in almost every corner of the world. 24. You mustn’t use this machine after 5:30 p.m. This machine mustn't be used after 5:30 pm. 25. After class, one of the students always erases the chalk board. After class, the chalkboard is always erased by one of the students

Dấu này * là dấu nhân

Một năm rồi không có ai trả lời à 

THấy cx thương nhưng mk nhìn cái đề thì dài thật cx khó có ai có thời gian mà giải

a) 12/17 + 21/25 = 657/425

b) 4 - 205/811 = 3039/811

c) 12 . 21/25 = 252/25

d) 4 : 205/811 =  205/3244

a) 12/17 + 21/25 = 657/425

b) 4 - 205/811 = 3039/811

c) 12 . 21/25 = 252/25

d) 4 : 205/811 = 205/3244