a ) Ta có : \(\frac{x+11}{10}+\frac{x+21}{20}+\frac{x+31}{30}=\frac{x+41}{40}+\frac{x+101}{5}\) 

\(\Leftrightarrow\left(\frac{x+11}{10}-1\right)+\left(\frac{x+21}{10}-1\right)+\left(\frac{x+31}{30}-1\right)=\left(\frac{x+41}{40}-1\right)+\left(\frac{x+101}{50}-2\right)\)

\(\Leftrightarrow\frac{x+1}{10}+\frac{x+1}{20}+\frac{x+1}{30}=\frac{x+1}{40}+\frac{x+1}{50}\)

\(\Rightarrow\frac{x+1}{10}+\frac{x+1}{20}+\frac{x+1}{30}-\frac{x+1}{40}-\frac{x+1}{50}=0\)

\(\Leftrightarrow\left(x+1\right)\left(\frac{1}{10}+\frac{1}{20}+\frac{1}{30}-\frac{1}{40}-\frac{1}{50}\right)=0\)

Mà \(\left(\frac{1}{10}+\frac{1}{20}+\frac{1}{30}-\frac{1}{40}-\frac{1}{50}\right)\ne0\)

Nên x + 1 = 0

=> x = -1

còn b vs c thì sao ạ

\(\frac{x-20}{x-10}=\frac{x+40}{x+70}=\frac{-20-40}{-10-70}=\frac{6}{8}=\frac{3}{4}.\)

\(\Rightarrow4\cdot\left(x-20\right)=3\cdot\left(x-10\right)\Leftrightarrow4x-80=3x-30\Leftrightarrow x=50.\)

bn dinh thuy linh gioi that, toàn dung ngôn ngữ toán hoc nên bai lam rat ấn tuong

\(\frac{x-20}{x-10}=\frac{x+40}{x+70}\)

\(\Rightarrow\left(x-20\right)\left(x+70\right)=\left(x-10\right)\left(x+40\right)\)

\(\Rightarrow x^2+70x-20x-1400=x^2+40x-10x-400\)

\(\Rightarrow x^2+70x-20x-x^2-40x+10x=1400-400\)

\(\Rightarrow20x=1000\Rightarrow x=50\)

a, \(\left(7,5-x\right):\left(3,5+x\right)=5:6\)

\(\Leftrightarrow\frac{7,5-x}{3,5+x}=\frac{5}{6}\)

\(\Leftrightarrow6.\left(7,5-x\right)=5.\left(3,5+x\right)\)

\(\Leftrightarrow45-6x=17,5+5x\)

\(\Leftrightarrow45-17,5=5x+6x\)

\(\Leftrightarrow27,5=11x\)

\(\Leftrightarrow x=\frac{27,5}{11}=2,5\)

Vậy : \(x=2,5\)

b) Tương tự như câu a.

Chúc bạn học tốt nhé !!

a) (x + 15) : x = 4 : 3

=> x : x + 15 : x = \(\frac{4}{3}\)

=> 1 + 15 : x = \(\frac{4}{3}\)

=> 15 : x = \(\frac{4}{3}\)- 1 = \(\frac{1}{3}\)

=> x = 15 : \(\frac{1}{3}\)

=> x = 45

phượng quyên là otaku sa( hình đại diện so cute)