\(\frac{1}{6}=\frac{x}{18}\Rightarrow x=3\)

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

\(\frac{4}{-5}=\frac{x}{10}\Rightarrow x=-8\)

\(\frac{11}{5}=-\frac{22}{x}\Rightarrow x=-10\)

\(\frac{x}{8}=\frac{8}{x}\Rightarrow x^2=64\Rightarrow x=8\)

\(\frac{x}{-11}=-\frac{11}{x}\Rightarrow x^2=121\Rightarrow x=11\)

#H

\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+....+\frac{1}{x\left(x+1\right)}=\frac{2008}{2009}\)

\(=>\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+....+\frac{1}{x\left(x+1\right)}=\frac{2008}{2009}\)

\(=>\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{x}-\frac{1}{x+1}=\frac{2008}{2009}\)

\(=>1-\frac{1}{x+1}=\frac{2008}{2009}=>\frac{1}{x+1}=1-\frac{2008}{2009}=\frac{1}{2009}\)

=>x+1=2009

=>x=2008

Vậy x=2008

1/2+1/6+1/12+...+1/x*(x+1)=2008/2009

  1/1*2+1/2*3+1/3*4+...+1/x*(x+1)=2008/2009

   1-1/2+1/2-1/3+1/3-1/4+...+1/x-1/(x+1)=2008/2009

  1-1/x+1)=2008/2009

1/x+1=1-2008/2009

1/x+1=1/2009

nên x+1=2009

      x=2009-1

     x=2008 (tick nha)

A ) x = 5/24

B ) x = 7/15

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

\(\Rightarrow\left(x+1\right)\left(x+1\right)=-8.-2\)

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

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

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

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

Dấu \(\orbr{\begin{cases}\\\end{cases}}\)là dấu hoặc nhé !!! 

Chúc bạn học tốt !!!