100 x 7 + 10 x 2 + 9

= 700 + 10 x 2 + 9

= 700 + 20 + 9

= 720 + 9 

= 729

like nhé ! ^^

B.2,4 hoặc 4 

2)

BTklg=>mO2=mhht-mhhs

ppe:6*nKClO3+5*nKMnO4-4nO2=nCl2*2

BTng tử ng tố =>nAgCl=nCl2*2

=>mAg=mh***AgCl

ppe:nFe*3=nAg+nCl2*2

=>m=nM

\(\frac{4}{5}\)- \(\frac{3}{4}\)= \(\frac{16}{20}\)- \(\frac{15}{20}\)= \(\frac{1}{20}\)

Like nha ! ^_^

Chuyển sang câu gián tiếp:

9. The old man said :"I will take you to my house right now".

The old man said that he would be take to his house then.

17. The librarian said :"This book was lent to him weeks ago and he has only just returned it".

The librarian said that that book had lent to his weeks ago and he had returned it.

Chuyển sang câu trực tiếp:

8.They said that he had deserved their thanks for all be had done.

They said: " He was deserved our thanks for all was be done"

9.The manager assured them that he had would return before they left.

The manager assured their : " He will return before they left"

12. All who heard this said he was speak the truth.

All who heard this said : " He speaks the truth"

D

A

B

B

A

T-T-F-F-T-F-F-T

a) ĐKXĐ \(\Leftrightarrow\)\(\begin{cases}\sqrt{a}\ge0\\\sqrt{a}-1\ne0\\\sqrt{a}\ne0\\a-2\ne0\end{cases}\)\(\Leftrightarrow\)\(\begin{cases}a\ge0\\a\ne0\\a\ne1\\a\ne2\end{cases}\)\(\Leftrightarrow\begin{cases}a>0\\a\ne1\\a\ne2\end{cases}\)

b)\(A=\left[\frac{\left(\sqrt{a}-1\right)\left(a+\sqrt{a}+1\right)}{\sqrt{a}\left(\sqrt{a}-1\right)}-\frac{\left(\sqrt{a}+1\right)\left(a-\sqrt{a}+1\right)}{\sqrt{a}\left(\sqrt{a}+1\right)}\right].\frac{a-2}{a+2}\)

\(=\left(\frac{a+\sqrt{a}+1-a+\sqrt{a}-1}{\sqrt{a}}\right).\frac{a-2}{a+2}=\frac{2\sqrt{a}}{\sqrt{a}}\cdot\frac{a-2}{a+2}=\frac{2a-4}{a+2}\)

c)\(A=\frac{2a-4}{a+2}=\frac{2\left(a+2\right)-8}{a+2}=2-\frac{8}{a+2}\)

A đạt GTNN khi và chỉ khi \(\frac{8}{a+2}\) đạt GTLN khi và chỉ khi a+2 đạt giá trị nhỏ nhất 

Mà min a+2 là 2 khi a=0 suy ra Min A\(=2-\frac{8}{2}=-2\)

Vậy Min A là -2 khi a=0

Ta có :

Người thứ nhất : bắt tay với 9 người kia

Người thứ hai : bắt tay với 9 người kia 

Người thứ ba : ...

Suy ra, có tổng cộng : 9 x 10 = 90 cái bắt tay 

53 và 97