a. \(\frac{x+1}{2}=\frac{8}{x+1}\)

\(\Leftrightarrow\left(x+1\right).\left(x+1\right)=8.2\)

\(\Leftrightarrow\left(x+1\right)^2=16\)

\(\Leftrightarrow\left(x+1\right)^2=2^4\)

\(\Leftrightarrow\left(x+1\right)=2^2\)

\(\Leftrightarrow\left(x+1\right)=4\)

\(\Leftrightarrow x=4-1=3\)

b. \(x:\left(9\frac{1}{2}-\frac{3}{2}\right)=\frac{0,4+\frac{2}{9}-\frac{2}{11}}{1,6+\frac{8}{9}-\frac{8}{11}}\)

\(\Leftrightarrow x:\left(\frac{10}{2}-\frac{3}{2}\right)=\frac{0,4+0,2-0,18}{1,6+0,8-0,72}\)

\(\Leftrightarrow x:\frac{7}{2}=\frac{\frac{21}{50}}{\frac{42}{25}}\)

\(\Leftrightarrow x=\frac{\frac{21}{50}}{\frac{42}{25}}.\frac{7}{2}\Leftrightarrow x=\frac{1}{4}.\frac{7}{2}=\frac{7}{8}\)

a )  \(\frac{x+1}{2}=\frac{8}{x+1}\)

\(\Rightarrow\left(x+1\right).\left(x+1\right)=2.8\)

\(\Rightarrow\left(x+1\right)^2=16\)

\(\Rightarrow\orbr{\begin{cases}x+1=4\\x+1=-4\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=4-1\\x=-4-1\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=3\\x=-5\end{cases}}\)

Dấu " \(\orbr{\begin{cases}\\\end{cases}}\)là hoặc nha !!! 

a)\(\frac{x+1}{2}=\frac{8}{x+1}\)

\(\Rightarrow\left(x+1\right)^2=8\times2=16\)

\(\Rightarrow\left(x+1\right)^2=4^2\)

\(\Rightarrow x+1=4\)

\(\Rightarrow x=4-1=3\)

b)tớ ko biết làm . ~ sorry~

~chuk bn hok giỏi~

x:(19:2-3:2)=(2:5+2:9-2:11):(8:5+8:9-8:11)

x:8=2(1:5+1:9-1:11):8(1:5+1:9-1:11)

x:8=1:6

x=(1:6)8

x=4:3

vì không viết được phân số nên mình đành dùng dấu chia thông cảm

a) x = 3 hoặc -5

b) 2

a ) (x+1)²=16

=>x+1=4    (vì x là số tự nhiên nên x+1=-4 là ko thỏa mãn)

=>x=3

b)x=2 ( cậu quy đồng rồi tự giải , có gì ko hiểu thì hỏi riêng mình )

\(x\div\left(9\frac{1}{2}-\frac{3}{2}\right)=\frac{0,4+\frac{2}{9}-\frac{2}{11}}{1,6+\frac{8}{9}-\frac{8}{11}}\)

\(\Leftrightarrow x\div\left(\frac{19}{2}-\frac{3}{2}\right)=\frac{0,4+\frac{2}{9}-\frac{2}{11}}{4\left(0,4+\frac{2}{9}-\frac{2}{11}\right)}\)

\(\Leftrightarrow x\div\frac{16}{2}=\frac{1}{4}\)

\(\Leftrightarrow x\div8=\frac{1}{4}\)

\(\Leftrightarrow x=\frac{1}{4}\times8\)

\(\Leftrightarrow x=2\)

\(x:\left(9\frac{1}{2}-\frac{3}{2}\right)=\frac{0,4+\frac{2}{9}-\frac{2}{11}}{1,6+\frac{8}{9}-\frac{8}{11}}\)

 \(x:\left(\frac{19}{2}-\frac{3}{2}\right)=\frac{0,4+\frac{2}{9}-\frac{2}{11}}{1,6+\frac{8}{9}-\frac{8}{11}}\)

                         \(x:8=\frac{0,4+\frac{2}{9}-\frac{2}{11}}{1,6+\frac{8}{9}-\frac{8}{11}}\)

Xét : \(\frac{0,4+\frac{2}{9}-\frac{2}{11}}{1,6+\frac{8}{9}-\frac{8}{11}}=\frac{0,4+\frac{2}{9}-\frac{2}{11}}{4.0,4+4.\frac{2}{9}-4.\frac{2}{11}}\)\(=\frac{0,4+\frac{2}{9}-\frac{2}{11}}{4\left(0,4+\frac{2}{9}-\frac{2}{11}\right)}=\frac{1}{4}\)

Thay vào biểu thức có : \(x:8=\frac{1}{4}\)

                                      \(\Rightarrow x=\frac{1}{4}.8=2\)

\(x:\left(9\frac{1}{2}-\frac{3}{2}\right)=\frac{0,4+\frac{2}{9}-\frac{2}{11}}{1,6+\frac{8}{9}-\frac{8}{11}}\)

\(x:\left(\frac{19}{2}-\frac{3}{2}\right)=\frac{\frac{2}{5}+\frac{2}{9}-\frac{2}{11}}{\frac{8}{5}+\frac{8}{9}-\frac{8}{11}}\)

\(x:8=\frac{2\left(\frac{1}{5}+\frac{1}{9}-\frac{1}{11}\right)}{8\left(\frac{1}{5}+\frac{1}{9}-\frac{1}{11}\right)}\)

\(x:8=\frac{2}{8}\)

\(x=\frac{2}{8}.8\)

\(x=2\)

~ Hok tốt ~

\(c,\frac{x+1}{2}=\frac{8}{x+1}\)

\(\Rightarrow(x+1)(x+1)=2.8\)

\(\Rightarrow(x+1)^2=16\)

\(\Rightarrow(x+1)^2=4^2\)

\(\Rightarrow x+1=4\)

\(\Rightarrow x=4-1\)

\(\Rightarrow x=3\)

\(a,x-(\frac{50x}{100}+\frac{25x}{200})=11\frac{1}{4}\)

\(\Rightarrow x-\frac{50x+25x}{100}=\frac{45}{4}\)

\(\Rightarrow\frac{100x}{100}-\frac{75x}{100}=\frac{45}{4}\)

\(\Rightarrow\frac{100x-75x}{100}=\frac{1125}{100}\)

\(\Rightarrow25x=1125\)

\(\Rightarrow x=45\)

\(b,(x-5)\frac{30}{100}=\frac{200x}{100}+5\)

\(\Rightarrow\frac{30x}{100}-\frac{3}{2}=\frac{200x}{100}+5\)

\(\Rightarrow\frac{30x}{100}-\frac{200x}{100}=5+\frac{3}{2}\)

\(\Rightarrow\frac{-170x}{100}=\frac{13}{2}\)

\(\Rightarrow\frac{-170x}{100}=\frac{650}{100}\)

\(\Rightarrow-170x=650\)

\(\Rightarrow x=\frac{-65}{17}\)