*chứng minh AB = AE
xét tam giác vuông ABD và tam giác vuông AED, có: 
góc BAD = góc EAD (vì A là đường phân giác của tam giác ABC)
AD là cạnh chung
=> tam giác ABD = tam giác AED (ch-gn)
=> AB = AE (2 cạnh tương ứng)
*chứng minh DQ = CD
xét tam giác AEQ và tam giác ABC , có:
góc AEQ = góc ABC (= 90 độ)
AB = AE (câu a)
góc A là góc chung
=> tam giác AEQ = tam giác ABC (c-g-c)
=> QE = BC (1)
ta có: DC = BC - BD; DQ = QE - DE (2) 
lại có: DB = DE (vì tam giác ABD = tam giác AED) (3)
=> TỪ (1) (2) (3) => DC = DQ

gọi khối lượng 2 thanh kim loại là x (kg)

ta có: A = 9x; B = x

thể tích khối A là: \(\dfrac{9x}{2700}=\dfrac{x}{300}\)

thể tích khối B là: \(\dfrac{x}{7800}\)

tỉ số thể tích giữa khối A và khối B là: 

\(\dfrac{\dfrac{x}{300}}{\dfrac{x}{7800}}=\dfrac{x}{300}\cdot\dfrac{7800}{x}=\dfrac{7800}{300}=26\)

BÀI 4: gọi d là quãng đường AB 

thời gian dự định để đi từ A đến B là: \(t=\dfrac{d}{50}\)

thời gian đi 2/3 quãng đường là: \(t'=\dfrac{\dfrac{2}{3}d}{50}=\dfrac{2d}{150}=\dfrac{d}{75}\)

thời gian đi 1/3 quãng đường là: \(t''=\dfrac{\dfrac{d}{3}}{40}=\dfrac{d}{120}\)

tổng thời gian thực tế đi từ A đến B là: \(t'+t''=\dfrac{d}{75}+\dfrac{d}{120}\)

theo đề, thời gian thực tế đi chậm hơn 30p nên ta có: 

\(\dfrac{d}{75}+\dfrac{d}{120}=\dfrac{d}{50}+0,5\\ \dfrac{4d}{300}+\dfrac{2,5d}{300}=\dfrac{6d}{300}+0,5\\ \dfrac{6,5d}{300}=\dfrac{6d}{300}+0,5\\ 6,5d=6d+150\\ 6,5d-6d=150\\ 0,5d=150\\ d=300\)

vậy quãng đường AB dài 300km

mình làm lại câu h xíu

\(\dfrac{3}{8}\cdot x-\dfrac{1}{2}=\dfrac{3}{4}\\ \dfrac{3}{8}\cdot x=\dfrac{5}{4}\\ x=\dfrac{5}{4}:\dfrac{3}{8}=\dfrac{5}{4}\cdot\dfrac{8}{3}\\ x=\dfrac{10}{3}\)

\(\left(2\dfrac{2}{15}\cdot\dfrac{9}{17}\cdot\dfrac{3}{32}\right):\left(-\dfrac{3}{17}\right)\\ =\left(\dfrac{32}{15}\cdot\dfrac{9}{17}\cdot\dfrac{3}{32}\right)\cdot\left(-\dfrac{17}{3}\right)\\ =\dfrac{32}{15}\cdot\dfrac{9}{17}\cdot\dfrac{3}{32}\cdot\dfrac{-17}{3}\\ =\left(\dfrac{32}{15}\cdot\dfrac{3}{32}\right)\cdot\left(\dfrac{9}{17}\cdot\dfrac{-17}{3}\right)\\ =\dfrac{1}{5}\cdot\left(-3\right)=-\dfrac{3}{5}\)

đối với danh từ không xác định thì không nên đưa vào trong câu bị động

1 If you didn’t live so far away, we would visit you more often
2 If the book were not so expensive, I would buy it
3 If we could afford it, we would go out more often
4 If we had some money, we could go on the trip
5 If you don’t water these plants, they will die
6 If I didn’t have to work late tomorrow, I would join your party
7 If you don’t study harder, you won’t pass the final exam
8 If we had had more money, we could have bought that house
9 If I were free today, we could go to the beach
10 If the film weren’t so boring, they wouldn’t have to leave the theater now
11 If you don’t pass this exam, you won’t get the scholarship
12 In case it rains on your way home, bring a raincoat with you
13 If you don’t eat less meat, you’ll gain much weight
14 If I were you, I wouldn’t accept his invitation
15 Should you arrive at the office earlier than I do, please turn on the air-conditioner
16 Had he not died so young, he would be a famous musician by now
17 But for the rain, we would have a better crop
18 If I were you, I wouldn’t buy it
19 If he hadn’t had money, he wouldn’t have bought such a big house
20 If you don’t get a visa, you can’t visit the USA
21 As long as you arrive before eleven, I can meet you
22 If Peter didn’t eat so many chips, he wouldn’t be fat
23 If Robert hadn’t started smoking cigarettes, he wouldn’t have gotten a bad cough
24 Unless you like this one, I’ll bring you another
25 Unless she hurries, she’ll be late
26 If it hadn’t been for Jack’s help, I wouldn’t have been able to move this table
27 If it weren’t for Helen, the play would be a flop
28 If I hadn’t had you, I would have given up years ago
29 If she hadn’t had a visa, she couldn’t have come to that country
30 As long as you drive carefully, you can use my car
31 If she were rich, she would travel around the world
32 If you go right now, you will catch a bus
33 Should you see Peter, tell him he should be here at 8:00
34 If you were to find some buried treasure, what would you do
35 But for Paul’s interest, the project would have been abandoned
36 If you happen to find my wallet, could you let me know

🙂🙂