1. Why did Tim have to leave work early yesterday?

2. She phoned you at about 7 o’clock this morning but you

didn't answer

3. I knew Lan were very busy ,so I disturbed her.

4. Let’s go out .It isn't raining now

5. It’s usually dry here at this time of the year. It doesn't rain much.

6. They didn't go to work yesterday .

7.Did you have a good time last week?

8. Why did you go to bed so early last night ?

9. They visited me ten years ago.

a. \(A\in Z\Leftrightarrow\) \(\dfrac{a-1}{a+1}\in Z\) ( ĐKXĐ: a\(\ge\) 0; a\(\ne\) 1)

Ta có: \(\dfrac{a-1}{a+1}=\dfrac{a+1-2}{a+1}=\dfrac{a+1}{a+1}-\dfrac{2}{a+1}=1-\dfrac{2}{a+1}\)

Vì:\(1\in Z\Rightarrowđể1-\dfrac{2}{a+1}\in Zthì2⋮\left(a+1\right)hay\left(a+1\right)\inƯ_{\left(2\right)}=\left\{\pm1;\pm2\right\}\)

*) a+1=1 <=> a=0(TMĐK)

*) a+1= -1 <=> a= -2 (KTMĐK)

*) a+1=2 <=> a= 1(KTMĐK)

*) a+1= -2 <=> a= -3 (KTMĐK)

Vậy x\(\in\) {0} thì A\(\in Z\)

Diện tích mảnh đất đó là:

18x15=270 (m^2)

Diện tích làm nhà là:

270:100x20=54 (m^2)

Đ/S ....

**** mik nha

Đổi 1,25 = \(\frac{125}{100}=\frac{5}{4}\)

Coi số bé là 4 phần, số lớn là 5 phần vậy tổng số phần bằng nhau là :

4 + 5 = 9

Số lớn là :

20,34 : 9 x 5 = 11,3

Số bé là :

20,34 - 11,3 = 9,04

77. I will never forget what you have just told me.

78. They are preparing the Christmas dinner at the moment.

79. When I last stayed in Cairo, I rode to the Pyramids in a camel that my friend had borrowed the day before.

80. George has been working at the university so far.

81. I see that Tom is writing his composition.

82. He says that he will look for a job next week.

83. They think he was here last night.

84. He tell us that he has been to the mountains before.

85. He wants to do it before his father comes.

86. The student who answered the question is John.

87. This is the house that Jack built three years ago.

88. Mary was having dinner when her friend called.

1/ John has worked in the sports shop since January.
2/ My parents has lived next to the supermarket for two years.
3/ They have known their teacher for three months.
4/ She hasn't worn her new shoes since she bought them.
5/ The shop has sold computer games since 2005.

1/x²+4x+4-9y²

= (x²+4x+4)-9y²

= (x+2)²-(3y)²

= [(x+2)-3y][(x+2)+3y]

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

2/x²-2xy+y²-16

= (x²-2xy+y²)-16

= (x-y)²-4²

= [(x-y)-4][(x-y)+4]

= (x-y-4)(x-y+4)

a) (x-4)²-(x+3)(x-4)

= (x-4)(x-4)-(x+3)(x-4)

= (x-4)[(x-4)-(x+3)]

= (x-4)(x-4-x-3)

= -7(x-4)

b) 16-a²-2ab-b²

= 16-(a²+2ab+b²)

= 4²-(a+b)²

= [4-(a+b)][4+(a+b)]

= (4-a-b)(4+a+b)

c) 4x²-17x+13

= 4x²-4x-13x+13

= (4x²-4x)-(13x-13)

= 4x(x-1)-13(x-1)

= (x-1)(4x-13)

6x²+12x+6

= 6(x²+2x+1)

= 6(x+1)²

= 6(x+1)(x+1)

(x²-5x+1)²+2(5x-1)(x²-5x+1)+(5x-1)²

= [(x²-5x+1)+(5x-1)]²

= (x²-5x+1+5x-1)²

= (x²)²

= x⁴