Vì c<10 , d<10 nên c+d < 20

Do đó giá trị lớn nhất của c+d là 19 .Vậy c+d có chữ số tận cùng lớn nhất bằng 9. Theo đề bài c + d = 0 . Vậy c = d = 0

Ta có : \(\overline{ab40}+\overline{1760}=\overline{ef900}\) . Đặt phép tính dọc, ta tính ra được b = 1, a = 9

Vậy \(\overline{abcdef}=\overline{910010}\)

a/ \(25< 3^x< 250\Leftrightarrow3^2< 3^x< 3^6\Leftrightarrow2< x< 6\)

Chọn x trong khoảng trên được : x = 3 , x = 4 , x = 5

b/ \(\left(2x+1\right)^3=125\Leftrightarrow\left(2x+1\right)^3=5^3\Leftrightarrow2x+1=5\Leftrightarrow x=2\)

c/ \(100< 5^{2x-1}< 5^6\Leftrightarrow5^2< 5^{2x-1}< 5^6\Leftrightarrow2< 2x-1< 6\Leftrightarrow2< x< 4\)

Chọn x trong khoảng trên được x = 3

d/ \(x^{15}=x\) \(\Leftrightarrow\left[\begin{array}{nghiempt}x=0\\x=1\end{array}\right.\)

e/ \(\left(x-5\right)^4=\left(x-5\right)^6\Leftrightarrow\left(x-5\right)^4\left[1-\left(x-5\right)^2\right]=0\Leftrightarrow\left(x-5\right)^4\left(6-x\right)\left(x-4\right)=0\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}x=4\\x=5\\x=6\end{array}\right.\)

g/ \(3^{2x+2}=9^{5-x}\Leftrightarrow9^{x+1}=9^{5-x}\Leftrightarrow x+1=5-x\Leftrightarrow x=2\)

1. People in rural areas of Britain talk optimistically / more optimistically about the future than city people

2. In India, rural areas are more populary / popular know as the "countryside"

3. A village is less densely populated / more densely populated than a city

4. City people seem to react quickly / more quickly to change than country people

5. Medical help can be less easily / more easily abained in a city than in the countryside

6. A buffalo ploughs better / more well than a horse.

a/

Ta có : \(3^{420}=\left(3^4\right)^{105}=81^{105}\) ; \(4^{315}=\left(4^3\right)^{105}=64^{105}\)

Vì 81 > 64 nên ..................................

b/Ta có : \(\begin{cases}\left(x^2-4\right)^2\ge0\\\left(3y-2\right)^2\ge0\end{cases}\) \(\Rightarrow\left(x^2-4\right)^2+\left(3y-2\right)^2\ge0\)

Do đó dấu "=" xảy ra chỉ khi \(\begin{cases}\left(x^2-4\right)^2=0\\\left(3y-2\right)^2=0\end{cases}\) \(\Leftrightarrow\begin{cases}x=\pm2\\y=\frac{2}{3}\end{cases}\)

Dễ dàng chứng minh được MDNB là tứ giác nội tiếp vì góc BMN = góc BDN = 90 độ

=> Góc MDB = góc MNB

Ta có góc MBN + góc MDN = 90 độ , góc MDN + góc DCB = 90 độ

=> góc MBN = góc DCB = 45 độ

=> Tam giác MBN là tam giác vuông cân => BM = MN

1. Do you usually watch TV every night?

2. We should brush our teeth after night meals.

3. Let's make our school ground more attractive

4.There are very good juices

5.What shall we have for breakfast tomorrow?

6. What a beautiful dress she has!

7. What kind of food would you like for lunch?

8. I like durians very much and so does my father

9. You must wash the spinach more carefully in the future

10. Dr.Lien gave Ba some medicine to make him feel better

\(2A=6x+4y+\frac{12}{x}+\frac{16}{y}=3x+\frac{12}{x}+y+\frac{16}{y}+3x+3y\)

Áp dụng bất đẳng thức cô si cho 2 số dương, ta có:

\(3x+\frac{12}{x}\ge2.\sqrt{36}=12\)

\(y+\frac{16}{y}\ge2\sqrt{16}=8\)

Lại có\(x+y\ge6\Rightarrow3x+3y\ge18\)

Vậy \(2A\ge12+8+18\Leftrightarrow2A\ge38\Leftrightarrow A\ge19\)    \(a=19\Leftrightarrow x=2;y=4\)

Most of the houses were pulled down last month, but they hadn't touched (not / touch) the old shop at the corner yet.

Trông có vẻ cũng vui nhỉ ^^ Cho mình một vé nha :))

I - complete the sentences with the correct form of the words in brackets : 

1. In spring, the place is crowded with skiers

2. He was so sad because the film ended unhappily

II - Make a new sentences with a tag question which has the same meaning as the first sentence : 

1. They don't go to school on foot every day , do they?

2. She doesn't have a lot of friends in Ha Noi , does she?

3. He waited for hey until she came back , didn't he?

4. They have already spoken to her about the problem , haven't they?

5. She won't meet you this morning , will she?