a) 45' = 0,75h

Sau 45' xe thứ nhất đi được quãng đường dài là:

42 . 0,75 = 31,5 ( km)

Sau 45' xe thứ 2 đi được quãng đường dài là:

36 . 0,75 = 27 ( km)

Sau 45' khoảng cách 2 xe là;

31,5 - 27 = 4,5 (km)

Vậy:...................................

b)

- 2 xe có gặp nhau

- Gọi thời gian kể từ lúc xuất phát đến lúc 2 xe gặp nhau là t (h)

Quãng đường xe thứ nhất đi được sau t là: S₁ = 42 . t = 42t

Quãng đường xe thứ nhất đi được sau t là: S₂ = 36 . t = 36t

Hai xe gặp nhau khi: S₁ + S₂ = S

=> 42t + 36t = 24

=> 78t = 24

=> t = \(\dfrac{4}{13}\left(h\right)\) = 52' 8 giây

=> 2 xe gặp nhau lúc: 7h + 52' 8 giây = 7 giờ 52 phút 8 giây

- Gặp ở đâu? Câu này thì chịu. Thời gian thế này tính kiểu gì?!

1 . Phuong is going to a party tonight ( What / she / wear ? )

=> What is she going to wear?

2 . I have just bought a poster . ( Where / you / put it ? )

=> Where are you going to put it?

3 . My parents are going to China next summer . ( How / thay / travel ? )

=> How are they going to travel?

4 . We are having a dinner party next Saturday . ( Who / you / invite ? )

=> who are you going to invite?

5 . They are meeting Tom at the airport . ( When / he / arrive ? )

=> When is he going to arrive?

6 . My sister has invited some friends home for lunch . ( What / she / cook ? )

=> What is she going to cook?

7 . I'm too busy to paint the door today . ( You / paint it / tomorrow ? )

=> How are you going to paint it tomorrow?

8 . Minh isn't going to visit his parents on Sunday. ( He / visit them / Sunday ? )

=> Is he going to visit them on Sunday?

Bài 2: 2 đường thẳng x và x' cắt nhau thế y ở đâu mà có xOy?

a) \(\left(3x-5\right)\left(x+4\right)=3x^2+12x-5x-20=3x^2+7x-20\)

b) \(\left(2x-3y\right)\left(2x+3y\right)=\left(2x\right)^2-\left(3y\right)^2=4x^2-9y^2\)

Ta có: \(\dfrac{a}{b}=\dfrac{9}{4}\Rightarrow\dfrac{a}{9}=\dfrac{b}{4}\Rightarrow\dfrac{a}{45}=\dfrac{b}{20}\)

\(\dfrac{b}{c}=\dfrac{5}{3}\Rightarrow\dfrac{b}{5}=\dfrac{c}{3}\Rightarrow\dfrac{b}{20}=\dfrac{c}{12}\)

Xét: \(\dfrac{a}{45}=\dfrac{b}{20}=\dfrac{c}{12}=k\Rightarrow\left\{{}\begin{matrix}a=45k\\b=20k\\c=12k\end{matrix}\right.\)

Thay \(\left\{{}\begin{matrix}a=45k\\b=20k\\c=12k\end{matrix}\right.\) vào \(\dfrac{a-b}{b-c}\)

Ta được: \(\dfrac{45k-20k}{20k-12k}=\dfrac{\left(45-20\right)k}{\left(20-12\right)k}=\dfrac{25k}{8k}=\dfrac{25}{8}\)

Vậy: .........................................

Cho dạng đúng động từ trong ngoặc 1 . My brother (buy) ......bought..... a computer last years 2 . She (not help) ......didn't help......her friends yesterday 3 . Do They often (go) .....go........ up the moutain ? 4 . There (be).....was...... a typhoon yesterday morning 5 . Why did he (stay) .......stay......up late last night ? 6 . My parent (work) ....are working .........on the farm now 7 . Lan (not usually) .....isn't usually ....... do her homework 8 . Where did they (buy) .......buy......there pens yesterday ? 9 . Who did they (live) ......live........with 5 years ago ? 10 . He and his friends (play) .........are playing......tennis now

A: Will you...(1)be...free this Sunday?

B: Yes, I...will(2)...?

a) \(\dfrac{16}{2^n}=2\Rightarrow2^n=\dfrac{16}{2}\Rightarrow2^n=8\)

Ta có: \(2^3=8\Rightarrow n=3\)

b) \(\dfrac{\left(-3\right)^n}{81}=-27\Rightarrow\left(-3\right)^n=\left(-27\right).81\)

\(\Rightarrow\left(-3\right)^n=-2187\)

Ta có: - 2187 = ( -3 ) ⁷

\(\Rightarrow n=7\)

c) \(8^n:2^n=4=\left(\dfrac{8}{2}\right)^n=4\Rightarrow4^n=4\)

\(\Rightarrow n=1\)

1.My house is (big)…………bigger… than yours.

2.This flower is (beautiful)………more beautiful……… than that one.

3.This is the (interesting)………most interesting……… book I have ever read.

4.Non-smokers usually live (long)……longer………… than smokers.

5.Which is the (dangerous)……most dangerous………… animal in the world?

6.A holiday by the sea is (good)……better………… than a holiday in the mountains.

7. It is strange but often a coke is (expensive)………more expensive ……… than a beer.

8.Who is the (rich)………richest……… woman on earth?

9. The weather this summer is even (bad)…………worse…… than last summer.

10. He was the (clever)………cleverest……… thief of all.