Bài 6:

\(A=3+\left(3^2+3^3\right)+\left(3^4+3^5\right)+...+\left(3^{2020}+3^{2021}\right)\\ A=3+3^2\left(1+3\right)+3^4\left(1+3\right)+...+3^{2021}\left(1+3\right)\\ A=3+4\left(3^2+3^4+...+3^{2021}\right)⋮̸4\left(3⋮̸4\right)\)

\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{3}{4}x+3y=6\\\dfrac{2}{3}x+3y=6\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{12}x=0\\\dfrac{1}{4}x+y=2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=0\\y=2\end{matrix}\right.\)

Bài 2: 

b: \(\Leftrightarrow x^2=10\)

hay \(x=\pm\sqrt{10}\)

1. how far is it from here to the nearest post office?

2 how far is it from new york to california?

3. how far is it from your house to your family store

4 how far is it from beijing to berlin

5 how far is it  from your hotel to the beach

1 How far is it from here to the nearest post office?

2 How far is it from New Yorn to California?

3 How far is it from your house to the your family store?

4 How far is it from Beijing to Berlin?

5 How far is it from your hotel to the beach?

Bài 3: Dựa vào những câu trả lời cho trước, hãy viết câu hỏi về khoảng cách.

1. How far is it from here to the nearest post office?

2. How far is it from New York to California?

3.How far is it from your house to your family store?

4.How far is it from Beijing to Berlin?

5.How far is it from your hotel to the beach?