\(xy-2x+y+1=0\\ x\left(y-2\right)+\left(y-2\right)=-3\\ \left(x+1\right)\left(y-2\right)=-3\)

Lập bảng

Vậy \(\left(x;y\right)\in\left\{\left(0;5\right);\left(2;3\right);\left(-2;-1\right);\left(-4;1\right)\right\}\)

Lập bảng

Vậy 

chúc bn học tốt nha

\(xy+3x-y=6\)

=> \(xy+3x-y-3=3\)

=> \(\left(xy+3x\right)-\left(y+3\right)=3\)

=> \(x\left(y+3\right)-\left(y+3\right)=3\)

=> \(\left(y+3\right)\left(x-1\right)=3\)

Mà x, y nguyên

=> \(x-1\)và \(y+3\)là số nguyên

=> \(\hept{\begin{cases}x-1=1\\y+3=3\end{cases}}\); \(\hept{\begin{cases}x-1=3\\y+3=1\end{cases}}\)và \(\hept{\begin{cases}x-1=-1\\y+3=-3\end{cases}}\)

=> \(\hept{\begin{cases}x=2\\y=0\end{cases}}\); \(\hept{\begin{cases}x=4\\y=-2\end{cases}}\)và \(\hept{\begin{cases}x=0\\y=-6\end{cases}}\)

Vậy cặp số nguyên (x;y) thỏa mãn là (2;0), (4;-2) và (0;-6)

Dạng này thì ta phân tích vế trái là 1 tích bên phải là 1 hằng số:
2x^2+3xy-2y^2=7 <=> 2x^2 + 4xy-xy-2y^2=7
<=> 2x(x+2y)- y(x+2y)=7 <=> (x+2y)(2x-y)=7
vì 7= 7.1=1.7=-1.(-7)=-7.(-1) nên ta có 4 trường hợp: 
x+2y 1 7 -7 -1
2x-y 7 1 -1 -7
x 0,2 1,8 -12,2 -3
y 0,4 2,6 -2,6 1
kết luận  loại loại loại thỏa mãn
Vậy x=-3; y=1

Ta có:
2x^2+3xy-2y^2=7
\Leftrightarrow 2x^2-xy+4xy-2y^2=7
\Leftrightarrow x(2x-y)+2y(2x-y)=7
\Leftrightarrow (2x-y)(x+2y)=7
Ta có: 2x-y, x+2y là nghiệm của 7
Nếu 2x-y=7, x+2y=1
\Rightarrow 2(2x-y)+x+2y=15
\Rightarrow 5x=15 \Rightarrow x=3, y=-1 (TM)
Tương tự:
Nếu 2x-y=1,x+2y=7 \Rightarrow x=1,8 , y=2,6 (KTM)
Nếu 2x-y=-1,x+2y=-7 \Rightarrow x=-1,8 , y=-2,6(KTM)
Nếu 2x-y=-7 , x+2y=-1\Rightarrow x=-3, y=1(tm)
Vậy (x;y) là (3;-1);(-3;1)

thôi thì đành tự giải vậy 

2¹³.5⁷=640000000

các chữ số của a là 6;4;0

Bài 1

Vietnam is famous for its several holiday and festival, especially Tet holiday. It takes place from the first day of the first month of the lunar calendar until at least the third day. Although occurring in short period of time, it is believed to be the most important and popular holiday in Vietnam. There are many special food are made so as to prepare for Tet meal such as: sky square cake, Vietnamese sausage, sky rice and jam. The food is thought to reflect Vietnam’s habit and custom as well as Vietnamese’s lifestyle. Besides, the meal has other dishes fish, vegetable to show the hope for a successful and prosperous new year. In term of customs, children’s receiving red envelop from the elder, visiting relative’s houses and going to church are popular activities. Giving lucky money is thought to bring children hope and health. Church is the symbol of peace; therefore, individual go there and pray for successive year. Traditionally, the house is designed with peach flower in the North and Ochna integerrima in the south part of Vietnam. Besides, the house as well as town are clear, decorative and beautiful as all are ready to start a new year. People have cozy atmosphere and enjoy joyful time with their family’s members. It’s high time for people living at different parts of country gathering and spending time together. Tet is a chance for one to come back home after many stress and pressure of studying and working environment. Tet is not simply a holiday, it is culture and habit of Vietnamese since its deep meaning is sacred and important. All in all, Tet includes not only joy but also long-standing event in people’s soul as it helps one grow up through experience.

~ học tốt ~

Bài 2:

Tet is a national and family festival. It is an occasion for every Vietnamese to have a good time while thinking about the last year and the next year. At Tet, spring fairs are organized, streets and public buildings are brightly decorated and almost all shops are crowded with people shopping for Tet. At home, every is tidied, special food is cooked,offerings of food, fresh water, flowers and betel are made on the family altar with burning joss- sks scenting the air. First-footing is made when the lucky visitor comes and children are given lucky money wrapped in a red tiny envelope. Tet is also a time for peace and love. During Tet, children often behave well and friends, relatives and neighbors give each other best wishes for the new year.

Tet holiday is celebrating on the fist day of the Lunar New Year.Some weeks before New Year , the Vietnamese clean their houses and repaint the walls.They also buy new clothes.One or two days before the festival,people make banh chung- the traditional cakes,and other goodies. On the New Ther'Eve, whole family for reguin dinner.Every members of the family should be present during the dinner.On the New Year Moring,the young members of family pay their respect to the elders. IN return they receive lucky money wrapped in red tiny evenlopes. Then people go to visit their neighbors,some friends and relatives.