Người đã xa mãi xa :))

- Điều kiện xác định: \(x\ne3\) và \(x\ne-3\)

\(B=\dfrac{2}{x-3}+\dfrac{5}{x+3}-\dfrac{12}{\left(x-3\right)\left(x+3\right)}\)

\(B=\dfrac{2\left(x+3\right)}{\left(x-3\right)\left(x+3\right)}+\dfrac{5\left(x-3\right)}{\left(x-3\right)\left(x+3\right)}-\dfrac{12}{\left(x-3\right)\left(x+3\right)}\)

\(B=\dfrac{2x+6+5x-15-12}{\left(x-3\right)\left(x+3\right)}\)

\(B=\dfrac{7x-21}{\left(x-3\right)\left(x+3\right)}\)

\(B=\dfrac{7\left(x-3\right)}{\left(x-3\right)\left(x+3\right)}\)

\(B=\dfrac{7}{x+3}\)

Để \(\dfrac{7}{x+3}\in Z\)

\(\Leftrightarrow x+3\inƯ\left(7\right)\)

\(\Leftrightarrow x+3\inƯ\left(\pm1;\pm7\right)\)

- \(x+3=1\Rightarrow x=-2\) (tm)

- \(x+3=-1\Rightarrow x=-4\) (tm)

- \(x+3=7\Rightarrow x=4\) (tm)

- \(x+3=-7\Rightarrow x=-10\) (tm)

Vậy có 4 giá trị của x để \(B\in Z.\)

Circle the best answer (A, B, C or D) to complete the passage.

London has a (1) _____ of about 7 million. It lies on the Thames River, where the Romans landed nearly 200 years ago. (2) ______ about 1,800 until World War II, London was the biggest city in the world, but now there are many cities which are much bigger.

London is famous (3) ______ many things. Tourists come from all over the world to visit its historic buildings, such as St. Paul’s Cathedral, which has a huge dome, and the Houses of Parliament, where you can see and hear the famous clock, Big Ben. They also come to visit its theatres, its museums, and its many shops, such as Harrods, (4) ______ you can buy anything.

(5) _____ many big cities, London has problems with traffic and pollution. Over one million use the London Underground a day, but there are still too many cars on the streets.

Question 3:

A. with

B. of 

C. at

D. for

Để làm sạch dung dịch đồng (II) nitrat Cu(N O 3 ) 2 có lẫn tạp chất bạc nitrat AgN O 3 . Ta dùng kim loại

A. Mg

B. Cu

C. Fe

D. Au

đề thiếu rồi bạn bạn sửa lại đi