xy-x-3y=-1

=>x(y-1)-3y+3=-1+3=2

=>x(y-1)-3(y-1)=2

=>(x-3)(y-1)=2

vì x,y thuộc Z nên x-3 thuộc Z, y-1 thuộc Z

ta có bảng:

x-3:    1

x:       4

y-1:     2

y:        3....(bn tự làm tiếp)

vậy 

The fraction 3/5 is pronounced _____.

A. third-fives

B. three-five

C. three over fifth 

D. three-fifths

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 25 to 29.

The warming of the Pacific Ocean has created weather patterns (25) _______ strongly affect the world. When the water is warm, the amount of rainfall in Indonesia and the surrounding regions decreases. Australia could (26) _______ experience a drought in many parts. On the other hand, Chile (which borders the Pacific Ocean) is preparing for (27) _______ rainstorms. In Pakistan and northwestern India, the weather pattern makes the rainy season weaker and makes the area much drier.

This happening is called El Nino and is used by weather forecasters to make long-range weather predictions. They also know that El Nino will unusually bring heavy rains to the southwestern part of the United States and make the central part of the country drier at the same time.

According to research, weather forecasters used to know about the coming weather with certainty. Now everything has become completely different.

El Nino itself used to be (28) ________. It would occur every two to seven years. But now, this weather pattern is becoming more frequent. We cannot say when and how often tornadoes or cyclones occur. Scientists are unsure of the reason for this (29) _______ on a global scale either.

Điền vào ô 28.

A. incredible

B. remarkable

C. predictable

D. notable

Vẽ góc xOy khác góc bẹt. Lấy A trên tia Ox,lấy B trên tia Oy (A, B khác điểm O). Hãy tìm một điểm C sao cho góc BOC kề bù với góc BOA. Kể tên các cặp góc kề bù đỉnh B.

Khử hết m gam CuO bằng  H 2 dư, thu được chất rắn X. Cho X tan hết trong dung dịch HNO 3 dư thu được 2,24 lít khí NO (sản phẩm khử duy nhất của N + 5 ). Giá trị của m là

A. 9,6

B. 8,0

C. 6,4

D. 12,0

Cho bốn đường thẳng xx'. yy', zz', tt' cắt nhau tại O trong đó x O y ^ = 90 ° ,    z O t ^ = 90 ° . Trong đó có bao nhiêu góc bẹt, bao nhiêu góc vuông, bao nhiêu góc nhọn, bao nhiêu góc tù?

sao bạn viết phân số đc vậy