Giúp với ạ, cần gấp lắm
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\(\dfrac{x}{27}=\dfrac{2}{9}-\dfrac{1}{3}\Rightarrow\dfrac{x}{27}=-\dfrac{1}{9}\Rightarrow\dfrac{x}{27}=\dfrac{-3}{27}\Rightarrow x=27\)
\(\dfrac{x}{27}=\dfrac{2}{9}-\dfrac{1}{3}=-\dfrac{1}{9}\Rightarrow x=-\dfrac{1}{9}.27=-3\).
a: Xét tứ giác ABDC có
M là trung điểm của BC
M là trung điểm của AD
Do đó: ABDC là hình bình hành
mà \(\widehat{BAC}=90^0\)
nên ABDC là hình chữ nhật
I.
1C 2B 3C 4B
II.
5C 6C 7C 8A 9D 10A 11C 12D 13A 14C 15A 16B 17B 18B 19C 20A
III.
21B 22A 23A 24C
IV.
25. On the second Sunday in May.
26. No, they aren't.
27. Greeting cards, gifts, a day of leisure, breakfast cooked by their families and served to them on a tray in bed and a plant.
28. In a restaurant or in one of their home.
29. Greeting cards and gifts.
V.
30. I wish I remembered her surname.
31. This popular TV program is watched by millions of people every week.
32. I suggest putting garbage bins around the schoolyard.
33. Not as many people smoke as they used to.
34. Although I tried to stop smoking, it was very difficult to do.
35. I was such a smoky bar that we left it.
VI.
35. Don't press the red button in any circumstances.
36. Although he was tired, he agreed to play tennis.
37. She finds it easy to study maths.
38. I will inform you immediately when I go home.
39. It wass nobody's fauly that the meeting was cancelled.
40. The gate was closed to stop children from running into the road.
VII.
41C 42A 43D 44D 45A 46B 47C 48B 49A 50C
Lời giải:
Đặt \(\sqrt[3]{5\sqrt{2}+7}=m; \sqrt[3]{5\sqrt{2}-7}=n\)
\(m^3-n^3=14\)
\(mn=1\)
\((a+b+c)^3=(m-n)^3=m^3-3mn(m-n)-n^3=14-3(m-n)\)
\(\Leftrightarrow (a+b+c)^3=14-3(a+b+c)\)
\(\Leftrightarrow (a+b+c)^3+3(a+b+c)-14=0\)
\(\Leftrightarrow (a+b+c)^2[(a+b+c)-2]+2(a+b+c)(a+b+c-2)+7(a+b+c-2)=0\)
\(\Leftrightarrow (a+b+c-2)[(a+b+c)^2+2(a+b+c)+7]=0\)
Dễ thấy biểu thức trong ngoặc vuông $>0$ nên $a+b+c-2=0$
$\Leftrightarrow a+b+c=2$
$ab+bc+ac=\frac{(a+b+c)^2-(a^2+b^2+c^2)}{2}=\frac{2^2-1}{2}=\frac{3}{2}$
5:
a: Xét ΔABD vuông tại D và ΔACE vuông tại E có
góc A chung
=>ΔABD đồng dạng với ΔACE
b; ΔABD đồng dạng với ΔACE
=>AD/AE=AB/AC
=>AD/AB=AE/AC
Xét ΔADE và ΔABC có
AD/AB=AE/AC
góc DAE chung
=>ΔADE đồng dạng với ΔABC
c: ΔADE đồng dạng với ΔABC
=>S ADE/S ABC=(AD/AB)^2=1/4
1. Why don't we go for picnic on the weekend ?
→ I suggest that we should go for a picnic on the weekend.
2. The weather was awful, but we enjoyed our outdoor party last night
→ Although the weather is awful, we enjoyed our party last night.
3. The music was gentle. We listened to it last night
→ The music, which was gentle, we listened to last night
4. This is Mr. Jones. He writes poetry
→ This is Mr. Jones, who writes poetry