Ta có: \(x-\frac{20}{11\cdot13}-\frac{20}{13\cdot15}-...-\frac{20}{53\cdot55}=\frac{3}{11}\)

\(\Leftrightarrow x-10\cdot\left(\frac{2}{11\cdot13}+\frac{2}{13\cdot15}+...+\frac{2}{53\cdot55}\right)=\frac{3}{11}\)

\(\Leftrightarrow x-10\cdot\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{53}-\frac{1}{55}\right)=\frac{3}{11}\)

\(\Leftrightarrow x-10\cdot\left(\frac{1}{11}-\frac{1}{55}\right)=\frac{3}{11}\)

\(\Leftrightarrow x-10\cdot\frac{4}{55}=\frac{3}{11}\)

\(\Leftrightarrow x-\frac{8}{11}=\frac{3}{11}\)

\(\Leftrightarrow x=\frac{3}{11}+\frac{8}{11}\)

\(\Leftrightarrow x=1\)

Vậy \(x=1\)thỏa mãn đề. 

các  bạn ơi mình đang cần gấp . Mình chỉ còn 20 phút thui .  HUHU

              Bài làm :

1) \(\frac{x+11}{4}=\frac{2x+4}{5}\)

\(\Leftrightarrow\left(x+11\right).5=4.\left(2x+4\right)\)

\(\Leftrightarrow5x+55=8x+16\)

\(\Leftrightarrow5x-8x=16-55\)

\(\Leftrightarrow-3x=-39\)

\(\Leftrightarrow x=\frac{-39}{-3}=\frac{39}{3}=13\)

2)\(\frac{x+4}{x+10}=\frac{3}{5}\)

\(\Leftrightarrow\left(x+4\right).5=\left(x+10\right).3\)

\(\Leftrightarrow5x+20=3x+30\)

\(\Leftrightarrow5x-3x=30-20\)

\(\Leftrightarrow2x=10\)

\(\Leftrightarrow x=\frac{10}{2}=5\)

3)\(\frac{x+8}{x+14}=\frac{2}{3}\)

\(\Leftrightarrow\left(x+8\right).3=\left(x+14\right).2\)

\(\Leftrightarrow3x+24=2x+28\)

\(\Leftrightarrow3x-2x=28-24\)

\(\Leftrightarrow x=4\)

\(a,\)\(x+\frac{4}{5.9}+\frac{4}{9.13}+\frac{4}{13.17}+...+\frac{4}{41.45}=-\frac{37}{45}\)

  \(x+\left(\frac{9-5}{5.9}+\frac{13-9}{9.13}+\frac{17-13}{13.17}+...+\frac{45-41}{41.45}\right)=-\frac{37}{45}\)

  \(x+\left(\frac{1}{5}-\frac{1}{9}+\frac{1}{9}-\frac{1}{13}+\frac{1}{13}-\frac{1}{17}+....+\frac{1}{41}-\frac{1}{45}\right)-\frac{37}{45}\)

 \(x+\left(\frac{1}{5}-\frac{1}{45}\right)=-\frac{37}{45}\)

 \(x+\frac{8}{45}=-\frac{37}{45}\)

\(x=-\frac{37}{45}-\frac{8}{45}\)

\(x=-1\)

thế phần b, c đâu bạn

\(A=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{2}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{11}-\frac{5}{9}+\frac{3}{7}-\frac{1}{5}\)

\(=\left(\frac{1}{5}-\frac{1}{5}\right)+\left(-\frac{3}{7}+\frac{3}{7}\right)+\left(\frac{5}{9}-\frac{5}{9}\right)+\left(-\frac{2}{11}+\frac{2}{11}\right)+\left(\frac{7}{13}-\frac{7}{13}\right)-\frac{9}{16}\)

\(=0+0+0+0+0+\frac{9}{16}=\frac{9}{16}\)

a)\(-\frac{2}{5}+\frac{2}{3}x+\frac{1}{6}x=-\frac{4}{5}\Leftrightarrow\frac{5}{6}x=-\frac{2}{5}\Leftrightarrow x=-\frac{12}{25}\)
Vậy nghiệm là x = -12/25

b)\(\frac{3}{2}x-\frac{2}{5}-\frac{2}{3}x=-\frac{4}{15}\Leftrightarrow\frac{5}{6}x=\frac{2}{15}\Leftrightarrow x=\frac{4}{25}\)
Vậy nghiệm là x = 4/25

c)\(\frac{x+1}{10}+\frac{x+1}{11}+\frac{x+1}{12}=\frac{x+1}{13}+\frac{x+1}{14}\)\(\Leftrightarrow\left(x+1\right)\left(\frac{1}{10}+\frac{1}{11}+\frac{1}{12}-\frac{1}{13}-\frac{1}{14}\right)=0\)
\(\Leftrightarrow x+1=0\left(\frac{1}{10}+\frac{1}{11}+\frac{1}{12}-\frac{1}{13}-\frac{1}{14}\ne0\right)\)\(\Leftrightarrow x=-1\)
Vậy nghiệm là x = -1
 

Cảm ơn bạnh nha. Chúc bạn buổi tối ấm =)))) <3

x=8 hoặc9 bn nhé mình đi đúng đó

\(\frac{4}{11}< \frac{x}{20}< \frac{5}{11}\)

=> \(\frac{80}{220}< \frac{11x}{220}< \frac{100}{220}\)

Suy ra \(11x\in B\left(11\right)\)mà \(80< 11x< 100\)nên \(11x\in88;99\)

Suy ra \(x\in8;9\)