" There is no place like my home " . I live in a small house . To me , I've got a wonderful house . From the outside , it looks rather old with brick wall and tile roof , but it's very comfortable and cool house . 
There are 5 rooms : a living room , 3 bedroom and a kitchen.
The living room isn't very small with a long table and four chairs . There's a tea-tray on it for my parents to drink tea every day and to welcome guests .
Next , the two bedrooms are near together and next to the living-room . One is my parent and one is mine and brother . My bedroom is the place I like most . There are some my paintings draw on the wall . There is a wardrobe next to the bed . On the wall an air - conditioner . That is the place I always put my stuffed crocodile . I like cooking , so kitchen is one of my favorite rooms , too . There is a gas table and a refrigerator in the kitchen . And there is a lot of food such as fruits , eggs and vegetables ... I can learn how to cook any time. where is this our reunion family every evening. the garden behind my house are many flowers blooming by the daily care of my mother. house is the most peaceful place where every member gathers after a hard work day . I love my house very much.

Cho n số: x₁ ; x₂ ; x₃ ;..; x_n với x_k = 1 hoặc x_k = -1 với k thuộc \(\hept{\begin{cases}\\\end{cases}1;2;3;...;n}\)Chứng minh rằng: x₁x₂ + x₂x₃ + x₃x₄ + ... x_nx₁ = 0 thì n chia hết cho 4.