Ta có:

12=1.12=2.6=3.4=4.3=6.2.12.1

và: 2x-1 là Ư lẻ của 12

=> 2x-1 E {1;3}

+) 2x-1=1=>2x=1+1=2

=>x=1

=>y+3=12=>y=9

Vậy x=1;y=9

+) 2x-1=3=>2x=3+1=4=>x=4:2=2

=> y+3=12:3=4

=>y=1

Vậy y=1;x=2

Câu 1 đường link câu này mk lm tương tư nhé

https://olm.vn/hoi-dap/detail/155610978.html

Bài 1:

\(\frac{4}{12}+\frac{4}{20}+\frac{4}{30}+...+\frac{4}{306}\)

\(=4\cdot\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{306}\right)\)

\(=4\cdot\left(\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+...+\frac{1}{17\cdot18}\right)\)

\(=4\cdot\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{17}-\frac{1}{18}\right)\)

\(=4\cdot\left(\frac{1}{3}-\frac{1}{18}\right)\)

\(=4\cdot\left(\frac{6}{18}-\frac{1}{18}\right)\)

\(=4\cdot\frac{5}{18}\)

\(=\frac{10}{9}\)

Bài 2  :

\(\left(3x-4\right)-\left(6x+7\right)=8\)

\(3x-4-6x-7=8\)

\(\left(3x-6x\right)-\left(4+7\right)=8\)

\(-3x-11=8\)

\(-3x=8+11\)

\(-3x=19\)

\(x=19:\left(-3\right)\)

\(x=\frac{-19}{3}\)

Vậy  \(x=\frac{-19}{3}\)

b ) \(\left(\frac{4}{5}x+3\right):\left(-4\right)=\frac{1}{2}\)

\(\frac{4}{5}x+3=\frac{1}{2}\cdot\left(-4\right)\)

\(\frac{4}{5}x+3=-2\)

\(\frac{4}{5}x=\left(-2\right)-3\)

\(\frac{4}{5}x=-5\)

\(x=\left(-5\right):\frac{4}{5}\)

\(x=\left(-5\right)\cdot\frac{4}{5}\)

\(x=-4\)

Vậy   \(x=-4\)

k nha !

\(\frac{4}{12}\)+\(\frac{4}{20}\)+...+\(\frac{4}{306}\)=\(\frac{4}{3.4}\)+\(\frac{4}{4.5}\)+...+\(\frac{4}{17.18}\)=4(\(\frac{1}{3}\)-\(\frac{1}{4}\)+\(\frac{1}{4}\)-\(\frac{1}{5}\)+...+\(\frac{1}{17}\)-\(\frac{1}{18}\))

                                                                                                  =4(\(\frac{1}{3}\)-\(\frac{1}{8}\))=4.\(\frac{5}{24}\)=\(\frac{5}{6}\)

Cảm ơn 2 bạn đã giúp mình nha😜😝🙏🙏🙏🙏

a, Ta có : \(\frac{x+1}{2}+\frac{x-2}{4}=1-\frac{2\left(x-1\right)}{3}\)

=> \(\frac{6\left(x+1\right)}{12}+\frac{3\left(x-2\right)}{12}=\frac{12}{12}-\frac{8\left(x-1\right)}{12}\)

=> \(6\left(x+1\right)+3\left(x-2\right)=12-8\left(x-1\right)\)

=> \(6x+6+3x-6=12-8x+8\)

=> \(17x=20\)

=> \(x=\frac{20}{17}\)

b, Ta có : \(\frac{5x-1}{6}+x=\frac{6-x}{4}\)

=> \(\frac{5x-1+6x}{6}=\frac{6-x}{4}\)

=> \(4\left(11x-1\right)=6\left(6-x\right)\)

=> \(44x-4-36+6x=0\)

=> \(\)\(50x=40\)

=> \(x=\frac{4}{5}\)

c, Ta có : \(\frac{5\left(1-2x\right)}{3}+\frac{x}{2}=\frac{3\left(x-5\right)}{4}-2\)

=> \(\frac{20\left(1-2x\right)}{12}+\frac{6x}{12}=\frac{9\left(x-5\right)}{12}-\frac{24}{12}\)

=> \(20\left(1-2x\right)+6x=9\left(x-5\right)-24\)

=> \(20-40x+6x-9x+45+24=0\)

=> \(43x=89\)

=> \(x=\frac{89}{43}\)

\(\frac{2^{12}.3^5-4^6.81}{\left(2^2.3\right)^6+8^4.3^5}\)

\(=\frac{2^{12}.3^5-2^{12}.3^4}{2^{12}.3^6+2^{12}.3^5}\)

\(=\frac{2^{12}.\left(3^5-3^4\right)}{2^{12}.\left(3^6+3^5\right)}\)

\(=\frac{3^5-3^4}{3^6+3^5}=\frac{3^4.\left(3-1\right)}{3^5\left(3+1\right)}\)

\(=\frac{3^4.2}{3^5.4}=\frac{3^4.2}{3^4.3.4}=\frac{2}{12}=\frac{1}{6}\)

P/s: Hoq chắc ạ (: Ms lp 6 lm đại

\(\frac{x}{2}=\frac{y}{3}\)

\(\Leftrightarrow\frac{x}{8}=\frac{y}{12}\)(1)

\(\frac{y}{4}=\frac{z}{5}\)

\(\Leftrightarrow\frac{y}{12}=\frac{z}{15}\)(2)

Từ (1) (2)

 \(\Rightarrow\frac{x}{8}=\frac{y}{12}=\frac{z}{15}=\frac{x+y-z}{8+12-15}=\frac{10}{5}=2\)

\(\Rightarrow\hept{\begin{cases}x=2.8\\y=2.12\\z=2.15\end{cases}\Rightarrow}\hept{\begin{cases}x=16\\y=24\\z=30\end{cases}}\)

=>2/2.3+2/3.4+2/4.5+............+2/x.(x+1)=2007/2019

=>2(1/2.3+1/3.4+1/4.5+.......+1/(x+1))=2007/2019

=>2(1/2-1/3+1/3-1/4+1/4-1/5+.....+1/x-1/x+1)=2007/2019

=>2(1/2-1/2x+1)=2007/2019

=>1-2/x+1=2007/2009=>2/x+1=1-2007/2019=12/2019

=>x+1=336,5.Vay x=335,5

\(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{2}{x\left(x+1\right)}\)\(=\frac{2007}{2019}\)

\(\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+...+\frac{2}{x\left(x+1\right)}=\frac{2007}{2019}\)

\(2\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{x.\left(x+1\right)}\right)\)\(=\frac{2007}{2019}\)

\(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{x}-\frac{1}{x+1}\)\(=\frac{2007}{2019}\div2\)

\(\frac{1}{2}-\frac{1}{x+1}=\frac{669}{1346}\)

\(\frac{1}{x+1}=\frac{1}{2}-\frac{669}{1346}\)

\(\frac{1}{x+1}=\frac{2}{673}\)

\(\frac{2}{\left(x+1\right)2}=\frac{2}{673}\)

\(\Rightarrow\left(x+1\right)2=673\)

\(\Rightarrow x+1=673\div2\Rightarrow x+1=336,5\Rightarrow x=336,5-1=335,5\)

b1 dễ quá 

vậy thì bạn giải đi

ai giải nhanh hộ mình đc ko,mình cần gấp,tồi hôm nay trước 10h15 mong mọi người giải nhanh hộ mình