Làm hộ em bài 11 12 13
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
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
![](https://rs.olm.vn/images/avt/0.png?1311)
= 12/11
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 12:
a: Xét ΔABM và ΔACN có
AB=AC
\(\widehat{ABM}=\widehat{ACN}\)
BM=CN
Do đó: ΔABM=ΔACN
![](https://rs.olm.vn/images/avt/0.png?1311)
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.
\(=\frac{(3-\sqrt{x})(3\sqrt{x}-2)+(5\sqrt{x}+7)(3\sqrt{x}+4)}{(5\sqrt{x}+7)(3\sqrt{x}-2)}-\frac{42\sqrt{x}+34}{(5\sqrt{x}+7)(3\sqrt{x}-2)}\)
\(=\frac{12x+52\sqrt{x}+22}{(5\sqrt{x}+7)(3\sqrt{x}-2)}-\frac{42\sqrt{x}+34}{(5\sqrt{x}+7)(3\sqrt{x}-2)}\)
\(=\frac{12x+10\sqrt{x}-12}{(5\sqrt{x}+7)(3\sqrt{x}-2)}=\frac{2(3\sqrt{x}-2)(2\sqrt{x}+3)}{(5\sqrt{x}+7)(3\sqrt{x}-2)}=\frac{2(2\sqrt{x}+3)}{5\sqrt{x}+7}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
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
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
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
11.
Gọi độ dài quãng đường AB là x (km) với x>0
Thời gian người đó đi từ A đến B: \(\dfrac{x}{30}\) giờ
Thời gian người đó đi từ B về A: \(\dfrac{x}{40}\) giờ
Do thời gian về ít hơn thời gian đi là 45 phút \(=\dfrac{3}{4}\) giờ nên ta có pt:
\(\dfrac{x}{30}-\dfrac{x}{40}=\dfrac{3}{4}\)
\(\Leftrightarrow\dfrac{x}{120}=\dfrac{3}{4}\)
\(\Rightarrow x=90\left(km\right)\)
12.
Đổi \(3h20'=\dfrac{10}{3}h\)
Gọi vận tốc của cano là x (km/h) với x>0
Vận tốc cano kém vận tốc ô tô là 17km/h nên vận tốc ô tô là: \(x+17\) (km/h)
Quãng đường cano đi trong 3h20': \(\dfrac{10}{3}x\) (km)
Quãng đường ô tô đi trong 2h: \(2\left(x+17\right)\) (km)
Do quãng đường sông ngắn hơn đường bộ là 10km nên ta có pt:
\(2\left(x+17\right)-\dfrac{10x}{3}=10\)
\(\Leftrightarrow-\dfrac{4}{3}x=-24\)
\(\Leftrightarrow x=18\)