Gọi số bước mà anh Sơn, chị Hà lần lượt đi được trong 1 phút là `x;y` (bước)

Điều kiện: `x;y ∈ N`*

Do nếu đi trong 2 phút thì anh Sơn bước nhiều hơn chị Hà 20 bước nên: 

`2(x - y) = 20`

`=> x - y = 10 (1) `

Nếu chị Hà đi trong 5 phút, anh Sơn đi trong 3 phút thì số bước chị Hà nhiều hơn anh Sơn là 160 bước nên: 

`5y - 3x = 160 (2)`

Từ (1)(2) ta có hệ phương trình: 

`{(x - y = 10),(5y - 3x = 160):}`

`<=> {(x = 105),(y=95):}` (Thỏa mãn)

Vậy số bước mà anh Sơn, chị Hà lần lượt đi được trong 1 phút là 105 và 95 bước

Trong 1 giờ anh Sơn đi được: `105 . 60 = 6300` (bước) -> Đủ chỉ tiêu

Trong 1 giờ chj Hà đi được: `95 . 60 = 5700` (bước) -> Chưa đủ chỉ tiêu

Vậy ...

Bài giải

có nhầm không vậy bạn? Kháng chiến chống quân xâm lược Thanh chứ nhỉ?

Most young people spend time on part-time work.

My students have so far found English to be the most important subject.

If you wish to live better, you should spend time studying economically.

Experience is so necessary that you may get a job without many things but being experienced.

It is supposed that your good English will always be an advantage in spite of your age.

Few people knew before that studying English carefully is the best way to prepare for the future.

It always takes a long time to master a subject such as English.

It has cost me much money by now to find myself feeling stupid without English.

1.Most of young people/spend/time/part-time work

Most of young people spend time on part-time work

2.My students/ so far/find/English/ most important

My students have so far found English the most important

3.If/ you/wish/live/ better/ you/ spend/time/ economically

If you wish to live better, you should spend time economically

4. Experience/ so necessary/that/ you/may/get/job/without many things/but being experienced

Experience is so necessary that you may get a job without many things but being experienced

I. Write in different ways

 1.The snow is so thick that vehicles have to wait a long time.

The snow is too thick for vehicles to go on.

Vehicles are prevented from going on due to thick snow.

If there were no thick snow, vehicles would not wait long.

Unless there is thick snow, vehicles can go on. 

2. This film is too long for my grandmother to see to the end.

The film is so long that my grandmother cannot see it to the end.

My grandmother can't see the film as it is very long.

If the film were not very long, my grandmother could see it to the end.

Unless the film is very long, my grandmother can see it to the end. 

II. Write in another way with the same meaning

1.I would rather not go to school on foot in this cold weather.

2.I would rather he do housework for me than study.

3.I would rather go out than stay home with these children.

4.The puzzle is easy enough for a smart boy to solve quickly.

5.The road is too narrow for even a bus to stop for a while.

1.the snow/ so thick/vehicles/ have/ wait/long

The snow is so thick that the vehicles have to wait too long 

=snow/ too thick/for/vehicles/ go on

The snow is too thick for the vehicles to go on

=vehicles/ prevented/ going on/ thick snow

The vehicles are prevented from going on the thick snow

=If/ there/ no thick snow/vehicles/not/ wait/long

If there were no thick snow, the vehicles wouldn't have to to wait for long

=Unless/there/ thick snow/vehicles/ go on

Unless there were thick snow, the vehicles would go on 

II. Write in another way with the same meaning

1.I/rather/not go/school/ on foot/ this cold weather

I would rather not go to school on foot in this cold weather 

=I/ prefer/ ride/bike/school/ this cold weather

I prefer riding a bike to school in this cold weather

2.I/ rather/he/ do/ housework/ for me/ study

I would rather he did the housework for me to study

=I/ prefer/him/do/ housework/ for me/ study

I prefer him to do the housework for me to study

3.I/ rather/ go gut/ than/stay/home/together/ these children

I would rather go out than stay at home together with these children

=I/ prefer/ go out/to/stay/home/together/ these children

I prefer going out to staying at home together with these children

4. The puzzle/ easy enough/for/ smart boy/ solve/ quickly

The puzzle is easy enough for the smart boy to solve quickly

=smart boy/ can solve/ puzzle/for/it/ very easy

The smart boy can solve the puzzle for it is very easy  

5.road/too narrow/ even a bus/ stop/ a while

The road is too narrow for even a bus to stop for a while

=Even a bus/not/stop/ a while/ because/ road/ very narrow

Even a bus can't stop for a while because the road is very narrow

Xét ΔEDC có AB//DC

nên \(\dfrac{EA}{AD}=\dfrac{EB}{BC}\)

mà AD=BC

nên EA=EB

Ta có: EA+AD=ED

EB+BC=EC

mà EA=EB và AD=BC

nên ED=EC

=>ΔEDC cân tại E

`2,25 - 2,(3) = 9/4 - 7/3 = 27/12 - 28/12 = -1/12 = -0,08(3) = -0,083`

Ta có phép tính:

\(2,25-2,\left(3\right)\)

\(=0,25-0,\left(3\right)\)

\(=\dfrac{1}{4}-\dfrac{1}{3}\)

\(=-\dfrac{1}{12}=-0,0833...\)

Làm tròn kết quả của phép tính \(2,25-2,\left(3\right)\) đến phần nghìn ta được -0,083.

\(2,25-2,\left(3\right)\\ =\dfrac{9}{4}-\dfrac{7}{3}\\ =\dfrac{27}{12}-\dfrac{28}{12}\\ =-\dfrac{1}{12}\\ =-0,08\left(3\right)\)
Làm tròn kết quả đến hàng phần nghìn được: \(-0,083\)

`2xy - 6x - 5y - 18 = 0`

`=> 2x(y - 3) = 5y + 18`

`=> 2x = (5y + 18)/(y-3)` với `y ne 3`

`=> 2x = (5y - 15 + 33)/(y-3) `

`=> 2x = 5 + 33/(y-3) `

Do `  2x` là số nguyên `=> 33/(y-3)` là số nguyên

`=> 33 vdots y - 3`

`=> y - 3 in Ư(33) = {-33;-11;-3;-1;1;3;11;33}`

Ta có bảng giá trị: 

Vậy ...

`A = 2x^2 - 2x`

`= 2(x^2 - x)`

`= 2(x^2 - 2 x . 1/2 + 1/4 - 1/4) `

`= 2(x- 1/2)^2 - 1/2`

Do `(x- 1/2)^2 >=0` với mọi `x`

`=> 2(x- 1/2)^2 >=0` với mọi `x`

`=> 2(x- 1/2)^2 - 1/2 > = -1/2` với mọi `x`

Dấu = có khi: 

`(x - 1/2)^2 = 0`

`<=> x - 1/2 = 0`

`<=> x =1/2`

Vậy ...

`B = 2x^2 - 5x + 4`

`= 2 (x^2 - 5/2 . x + 2) `

`= 2 (x^2 - 2 . 5/4 . x + 25/16 + 7/16) `

`= 2 (x - 5/4)^2 + 7/8`

Do `2 (x - 5/4)^2 >= 0` với mọi x

`=> 2 (x - 5/4)^2 + 7/8 >= 7/8` với mọi x

Dấu = có khi: 

`(x - 5/4)^2 = 0`

`<=> x - 5/4 = 0`

`<=> x = 5/4`

Vậy ...

`C = x^2 + x + 2 `

`= x^2 + 2x . 1/2 + 1/4 + 7/4`

`= (x + 1/2)^2 + 7/4`

Do `(x + 1/2)^2 >=0` với mọi x

`<=>  (x + 1/2)^2 + 7/4 >= 7/4 ` với mọi x

Dấu = có khi: 

`(x + 1/2)^2 = 0`

`<=> x  + 1/2 = 0`

`=> x = -1/2`

Vậy ...