2) Ta có: \(B=\dfrac{\sqrt{x}}{\sqrt{x}-2}:\left(\dfrac{x-2}{x-4}-\dfrac{1}{\sqrt{x}+2}\right)\)

\(=\dfrac{\sqrt{x}}{\sqrt{x}-2}:\dfrac{x-2-\sqrt{x}+2}{\left(\sqrt{x}+2\right)\left(\sqrt{x}-2\right)}\)

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

\(=\dfrac{\sqrt{x}+2}{\sqrt{x}-1}\)

a: y=0; x=3

😟😟

A                   =      \(\dfrac{1}{2}\) + \(\dfrac{1}{4}\) + \(\dfrac{1}{8}\)+ \(\dfrac{1}{16}\) + \(\dfrac{1}{32}\) + \(\dfrac{1}{64}\)+......+\(\dfrac{1}{1024}\)

A \(\times\)2           = 1 + \(\dfrac{1}{2}\) + \(\dfrac{1}{4}\) + \(\dfrac{1}{8}\) + \(\dfrac{1}{16}\) + \(\dfrac{1}{32}\)+\(\dfrac{1}{64}\)+...+\(\dfrac{1}{512}\)

A\(\times\)2 - A     =   1 - \(\dfrac{1}{1024}\)

A               = \(\dfrac{1023}{1024}\)

B = \(\dfrac{1}{1\times2}\)+\(\dfrac{1}{2\times3}\)+\(\dfrac{1}{3\times4}\)+\(\dfrac{1}{4\times5}\)+...+\(\dfrac{1}{98\times99}\)+\(\dfrac{1}{99\times100}\)

B = \(\dfrac{1}{1}\) - \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) - \(\dfrac{1}{3}\)+ \(\dfrac{1}{3}\)-\(\dfrac{1}{4}\)+\(\dfrac{1}{4}\)-\(\dfrac{1}{5}\)+...+\(\dfrac{1}{98}\)-\(\dfrac{1}{99}\)+\(\dfrac{1}{99}\)-\(\dfrac{1}{100}\)

B = 1 - \(\dfrac{1}{100}\)

B = \(\dfrac{99}{100}\)

C= \(\dfrac{1}{6}\) + \(\dfrac{1}{12}\)+ \(\dfrac{1}{20}\)+ \(\dfrac{1}{30}\)+\(\dfrac{1}{42}\)+...+\(\dfrac{1}{90}\)+\(\dfrac{1}{110}\)

C = \(\dfrac{1}{2\times3}\) +\(\dfrac{1}{3\times4}\)+\(\dfrac{1}{4\times5}\)+\(\dfrac{1}{5\times6}\)+...+\(\dfrac{1}{9\times10}\)+\(\dfrac{1}{10\times11}\)

C = \(\dfrac{1}{2}\)-\(\dfrac{1}{3}\)+\(\dfrac{1}{3}\)-\(\dfrac{1}{4}\)+\(\dfrac{1}{4}\)-\(\dfrac{1}{5}\)+\(\dfrac{1}{5}\)-\(\dfrac{1}{6}\)+...+\(\dfrac{1}{9}\)-\(\dfrac{1}{10}\)+\(\dfrac{1}{10}\)-\(\dfrac{1}{11}\)

C = \(\dfrac{1}{2}\) - \(\dfrac{1}{11}\)

C = \(\dfrac{9}{22}\)

Bài 2: 

a: =>168x+20=6x-21

=>162x=-41

hay x=-41/162

b: \(\Leftrightarrow2\left(3x-8\right)=3\left(5-x\right)\)

=>6x-16=15-3x

=>9x=31

hay x=31/9

c: \(\Leftrightarrow4\left(x^2+8x-20\right)-\left(x+4\right)\left(x+10\right)=3\left(x^2+2x-8\right)\)

\(\Leftrightarrow4x^2+32x-80-x^2-14x-40-3x^2-6x+24=0\)

=>12x-96=0

hay x=8

bÌ NÀO BN 

Bài 1: 

a: =204-7=197

b: =900-1+1=900

c: \(=155-12\cdot9\cdot2^8=-27493\)

Bài 2: 

a:=>x=405:27=15

Today, I will tell you some things to make school greener-cleaner. Firstly, I will ask everyone not to throw rubbish in the school because it is the reason of air pollution. Secondly, I will advise everyone to plant trees and flowers in the school yard. Thirdly, I will ask my teacher to celebrate many activities to protect the environment. Finnaly, I will advise everyone not to damage trees and flowers.... If everyone try to protect the environment, the school will be greener.

- plant some trees

- don't throw trash on the street

- plant some flowers

- don't damage trees

- don't pick flowers

Mẫu ví dụ của mình. Chúc bạn học tốt !

thanks

Xét ΔOHA vuông tại H và ΔOKA vuông tại K có

OA chung

OH=OK

Do đó: ΔOHA=ΔOKA

Suy ra: AH=AK

hay AB=AC

P = (10.10².10³.10⁴...10⁹) : (10⁵.10¹⁰.10²⁵)

= 10¹⁺²⁺³⁺⁴⁺⁵⁺⁶⁺⁷⁺⁸⁺⁹ 10⁵⁺¹⁰⁺²⁵

= 10⁴⁵ : 10⁴⁰

= 10⁴⁵⁻⁴⁰

= 10⁵

= 100000

\(P=\left(10.10^2.10^3.10^4.....10^9\right):\left(10^5.10^{10}.10^{25}\right)\)

\(P=10^{45}:10^{40}\)

\(P=10^5\)