a: ĐKXĐ: x>=0; x<>1

b: Sửa đề: \(A=\left(\frac{\sqrt{x}-2}{x-1}-\frac{\sqrt{x}+2}{x+2\sqrt{x}+1}\right)\cdot\frac{x^2-2x+1}{2}\)

\(=\left(\frac{\sqrt{x}-2}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}-\frac{\sqrt{x}+2}{\left(\sqrt{x}+1\right)^2}\right)\cdot\frac{\left(x-1\right)^2}{2}\)

\(=\frac{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)-\left(\sqrt{x}+2\right)\left(\sqrt{x}-1\right)}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)^2}\cdot\frac{\left(\sqrt{x}-1\right)^2\cdot\left(\sqrt{x}+1\right)^2}{2}\)

\(=\frac{x-\sqrt{x}-2-\left(x+\sqrt{x}-2\right)}{1}\cdot\frac{\sqrt{x}-1}{2}=-\sqrt{x}\left(\sqrt{x}-1\right)\)

c: A>=0

=>\(-\sqrt{x}\left(\sqrt{x}-1\right)\ge0\)

=>\(\sqrt{x}\left(\sqrt{x}-1\right)\le0\)

=>\(0\le x<1\)

d: \(A=-\sqrt{x}\left(\sqrt{x}-1\right)\)

\(=-x+\sqrt{x}\)

\(=-x+\sqrt{x}-\frac14+\frac14=-\left(\sqrt{x}-\frac12\right)^2+\frac14\le\frac14\forall x\) thỏa mãn ĐKXĐ

Dấu '=' xảy ra khi \(\sqrt{x}-\frac12=0\)

=>\(\sqrt{x}=\frac12\)

=>x=1/4(nhận)

có j đâu

Có gì đâu mà gửi vậy?

a: Xét ΔABC vuông tại A có

\(\sin B=\frac{AC}{BC};\sin C=\frac{AB}{BC}\)

=>\(\frac{sinB}{\sin C}=\frac{AC}{BC}:\frac{AB}{BC}=\frac{AC}{AB}\)

b: Xét ΔADE vuông tại D và ΔAHB vuông tại H có

AD=AH

\(\hat{DAE}=\hat{HAB}\) (hai góc đối đỉnh)

Do đó: ΔADE=ΔAHB

c: ΔADE=ΔAHB

=>AE=AB

Xét ΔCAE vuông tại A và ΔCAB vuông tại A có

CA chung

AE=AB

Do đó: ΔCAE=ΔCAB

=>CE=CB

=>ΔCBE cân tại C

d: ΔCAE=ΔCAB

=>\(\hat{ACE}=\hat{ACB}\)

Xét ΔCIA vuông tại I và ΔCHA vuông tại H có

CA chung

\(\hat{ICA}=\hat{HCA}\)

Do đó: ΔCIA=ΔCHA

=>AI=AH

=>I thuộc (A;AH)

Xét (A;AH) có

AI là bán kính

CE⊥AI tại I

Do đó; CE là tiếp tuyến tại I của (A;AH)

\(n_{FeS_2}=\dfrac{240}{120}.80\%=1,6\left(mol\right)\)

PTHH: 4FeS₂ + 11O₂ --t^o--> 2Fe₂O₃ + 8SO₂

               1,6 -------------------------------> 3,2

2SO₂ + O₂ --t^o--> 2SO₃

3,2 --------------------> 3,2

SO₃ + H₂O ---> H₂SO₄

3,2 ----------------> 3,2

\(m_{ddH_2SO_4}=\dfrac{3,2.98}{49\%}=640\left(g\right)\)

4FeS2+11O2-to>2Fe2O3+8SO2

1,6----------------------------------3,2

2SO2+O2-to,V2O5->2SO3

3,2----------------------------3,2

SO3+H2o->H2SO4

3,2-----------------3,2

n FeS2=2 mol

H=80%

=>n FeS2=2.80%=1,6 mol

=>m H2SO4=3,2.98=313,6g

=>mdd=640g

=>B

a: Ta có: \(\frac{\sqrt{x}+1}{2\sqrt{x}-2}-\frac{\sqrt{x}-1}{2\sqrt{x}+2}-\frac{x+1}{1-x}\)

\(=\frac{\sqrt{x}+1}{2\left(\sqrt{x}-1\right)}-\frac{\sqrt{x}-1}{2\left(\sqrt{x}+1\right)}+\frac{x+1}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\)

\(=\frac{\left(\sqrt{x}+1\right)^2-\left(\sqrt{x}-1\right)^2+2\left(x+1\right)}{2\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\)

\(=\frac{x+2\sqrt{x}+1-x+2\sqrt{x}-1+2x+2}{2\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}=\frac{2x+4\sqrt{x}+2}{2\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\)

\(=\frac{x+2\sqrt{x}+1}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}=\frac{\left(\sqrt{x}+1\right)^2}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}=\frac{\sqrt{x}+1}{\sqrt{x}-1}\)

\(A=\left(\frac{\sqrt{x}+1}{2\sqrt{x}-2}-\frac{\sqrt{x}-1}{2\sqrt{x}+2}-\frac{x+1}{1-x}\right)\cdot\frac{x+2\sqrt{x}+1}{x+\sqrt{x}}\)

\(=\frac{\sqrt{x}+1}{\sqrt{x}-1}\cdot\frac{\left(\sqrt{x}+1\right)^2}{\sqrt{x}\left(\sqrt{x}+1\right)}=\frac{\left(\sqrt{x}+1\right)^2}{\sqrt{x}\left(\sqrt{x}-1\right)}\)

b: Thay \(x=7-2\sqrt6=\left(\sqrt6-1\right)^2\) vào A, ta được:

\(A=\frac{\left(\sqrt{\left(\sqrt6-1\right)^2}+1\right)^2}{\sqrt{\left(\sqrt6-1\right)^2}\cdot\left(\sqrt{\left(\sqrt6-1\right)^2}-1\right)}\)

\(=\frac{\left(\sqrt6-1+1\right)^2}{\left(\sqrt6-1\right)\left(\sqrt6-1-1\right)}=\frac{6}{\left(\sqrt6-1\right)\left(\sqrt6-2\right)}=\frac{6}{6-3\sqrt6+2}=\frac{6}{8-3\sqrt6}\)

\(=\frac{6\left(8+3\sqrt6\right)}{64-54}=\frac{6\left(8+3\sqrt6\right)}{10}=\frac{3\left(8+3\sqrt6\right)}{5}\)

c: A<0

=>\(\frac{\left(\sqrt{x}+1\right)^2}{\sqrt{x}\left(\sqrt{x}-1\right)}<0\)

=>\(\sqrt{x}-1<0\)

=>\(\sqrt{x}<1\)

=>0<x<1

.

Hút thuộc chứ ko pk là hút thuốc đou, đừng nhầm lẫn :)

1 Sue wishes she hadn't bought that new book

2 Unless you walk faster, you will be late

3 Carol spent 2 hours fixing the television sets

4 I make these handicrafts by myself 

5 If I were you, I would take the bus instead of the train

II

1 She doesn't have to get up early on Saturday

2 Children mustn't be left alone in car

3 John must explain this if he want his student to succeed

4 I have to file the report this week

5 We don't have to work overtime on Saturdays

6 You mustn't drive more than 25 mph in this zone

7 She didn't have to attend the presentation yesterday

8 She has to pick up her children at school

9 You don't have to arrive before 8

10 They had to visit the doctor yesterday as they didn't feel well