x/120=-7/24*-6/11

x/120=7/44

x=7*120:44

x=210/11

Không rõ đề lắm bạn ơi

câu hỏi của bạn có sai ko ạ

a) \(x=\dfrac{1}{2}+\dfrac{3}{4}\)

\(\Rightarrow x=\dfrac{2}{4}+\dfrac{3}{4}\\ \Rightarrow x=\dfrac{5}{4}\)

b) \(\dfrac{x}{5}=\dfrac{1}{2}-\dfrac{2}{3}\)

\(\Rightarrow\dfrac{x}{5}=\dfrac{3}{6}-\dfrac{4}{6}\)

\(\Rightarrow\dfrac{x}{5}=-\dfrac{1}{6}\)

\(\Rightarrow x=-\dfrac{1}{6}.5\)

\(\Rightarrow x=-\dfrac{5}{6}\)

c) \(x=\dfrac{1}{2}-\dfrac{2}{3}\)

\(\Rightarrow x=\dfrac{3}{6}-\dfrac{4}{6}\)

\(\Rightarrow x=-\dfrac{1}{6}\)

d) \(\dfrac{x}{3}=\dfrac{2}{3}-\dfrac{1}{7}\)

\(\Rightarrow\dfrac{x}{3}=\dfrac{14}{21}-\dfrac{3}{21}\)

\(\Rightarrow\dfrac{x}{3}=\dfrac{11}{21}\)

\(\Rightarrow x=\dfrac{11}{21}.3\)

\(\Rightarrow x=\dfrac{33}{21}\)

1)

a) 21/23 x 5/11 x 4/35

= \(\frac{21.5.4}{23.11.35}\)

= \(\frac{7.3.5.4}{23.11.5.7}\)

= \(\frac{3.4}{23.11}\)    ( ta đã rút gọc 7 và 5 )

= \(\frac{12}{253}\)

b) 26 x 13/42 : 13

= \(\frac{26.13}{42.13}\)

= \(\frac{13.2.13}{21.2.13}\)

= \(\frac{13}{21}\)

c) 5/9 : 2/9 + 4/9 : 2/3

= \(\frac{5.9}{9.2}+\frac{4.3}{9.2}\)

= \(\frac{5}{2}+\frac{2.2.3}{3.3.2}\)

= \(\frac{5}{2}+\frac{2}{3}\)

= \(\frac{19}{6}\)

2 ) tìm x

a ) 2 - x = 1/3 + 1/6

      2 - x = 1/2

      x = 2 - 1/2 

    x = 3/2

b ) x + 5/8 = 1 + 3/4

     x + 5/8 = 7/4 

      x = 7/4 - 5/8 

       x = 9/8

3) 

a)  x < 3/4 + 4/5

=> x < 31/20 

=> x = 1

b) 1/2 + 3/5 < x < 5/4

  => 11/10   < x < 5/4

ta quy đồng phân số 11/10 và 5/4

\(\frac{11}{10}=\frac{11.4}{10.4}=\frac{44}{40}\)

\(\frac{5}{4}=\frac{5.10}{4.10}=\frac{50}{40}\)

=> 44/40 < x <  50/40

=> x không thỏa mãn 

plp]l]

A=1/1.2+1/2.3+...1/x =49/50

A=1-1/2+1/2-1/3+...+1/x-1-1/x=49/50

A=1-1/x=49/50

A=50/50-1=x=49/50

x=1/50

\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{x}=\frac{49}{50}\)

\(\Rightarrow\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{x\left(x-1\right)}=\frac{49}{50}\)

\(\Rightarrow1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{x-1}-\frac{1}{x}=\frac{49}{50}\)

\(\Rightarrow1-\frac{1}{x}=\frac{49}{50}\)

\(\Rightarrow\frac{1}{x}=\frac{1}{50}\)

\(\Rightarrow x=50\)

\(A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{x}\)

\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{\left(n-1\right)n}\) với \(\left(n-1\right)n=x\)

\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{n-1}-\frac{1}{n}\)

\(A=1-\frac{1}{n}\)

Mà \(A=\frac{49}{50}\)

\(\Rightarrow1-\frac{1}{n}=\frac{49}{50}\)

              \(\frac{1}{n}=1-\frac{49}{50}\)

              \(\frac{1}{n}=\frac{1}{50}\)

\(\Rightarrow n=50\)

Có \(x=\left(n-1\right)n\)

\(\Rightarrow x=\left(50-1\right)50\)

    \(x=49.50\)

    \(x=2450\)

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củ6e

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a)-3 phần 5 = 6 phần -10

b) 3 phần -7 = -33 phần 77

c) 4 phần 3 = 4 phần 3

d) 2 phần 7 = 2 phần 7

\(\frac{x}{5}=\frac{6}{-10}\rightarrow x=6\cdot\left(-10\right):5=12\)

\(\frac{3}{y}=\frac{-33}{77}\rightarrow y=77\cdot3:\left(-33\right)=-7\)

\(\frac{x}{3}=\frac{4}{y}\rightarrow x,y\in UC\left(3,4\right)\)

ƯC(3,4) Ta có bảng sau