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]

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

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

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

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

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

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

a: \(A=\left(\dfrac{2+x}{2-x}-\dfrac{4x^2}{x^2-4}-\dfrac{2-x}{2+x}\right):\dfrac{2\left(x-3\right)}{2-x}\)

\(=\dfrac{4+4x+x^2+4x^2-\left(2-x\right)^2}{\left(2-x\right)\left(2+x\right)}\cdot\dfrac{2-x}{2\left(x-3\right)}\)

\(=\dfrac{5x^2+4x+4-4+4x-x^2}{\left(2+x\right)}\cdot\dfrac{1}{2\left(x-3\right)}\)

\(=\dfrac{4x^2+8x}{x+2}\cdot\dfrac{1}{2\left(x-3\right)}=\dfrac{4x\left(x+2\right)}{2\left(x+2\right)}\cdot\dfrac{1}{x-3}=\dfrac{2x}{x-3}\)

b: |x-2|=2

=>x-2=2 hoặc x-2=-2

=>x=0(nhận) hoặc x=4(nhận)

Khi x=0 thì \(A=\dfrac{2\cdot0}{0-3}=\dfrac{-2}{3}\)

Khi x=4 thì \(A=\dfrac{2\cdot4}{4-3}=8\)

c: A>0

=>x/x-3>0

=>x>3 hoặc x<0

=>x>3

\(\frac{x}{3\frac{1}{2}.2\frac{2}{3}}=\frac{9}{56}\Rightarrow\frac{x}{\frac{7}{2}.\frac{8}{3}}=\frac{9}{56}\Rightarrow x=\frac{9}{56}.\frac{28}{3}=\frac{3}{2}\)

\(x:\left(3\frac{1}{2}.2\frac{2}{3}\right)=\frac{9}{56}\)

\(x:\left(\frac{7}{2}.\frac{8}{3}\right)=\frac{9}{56}\)

\(x:\left(\frac{7.4}{3}\right)=\frac{9}{56}\)

\(x.\frac{3}{28}=\frac{9}{56}\)

\(x=\frac{9}{56}.\frac{28}{3}=\frac{3}{2}\)

Vậy \(x=\frac{3}{2}\)

\(\left(\frac{2}{3}+\frac{1}{3}:\frac{3}{4}+\frac{5}{9}\right).y-3=25\%+\frac{7}{4}\)

\(\Rightarrow\left(\frac{2}{3}+\frac{4}{9}+\frac{5}{9}\right).y-3=\frac{1}{4}+\frac{7}{4}\)

\(\Rightarrow\left(\frac{2}{3}+1\right).y-3=2\)

\(\Rightarrow\frac{5}{3}.y-3=2\)

\(\Rightarrow y-3=2:\frac{5}{3}\)

\(\Rightarrow y-3=\frac{6}{5}\)

\(\Rightarrow y=\frac{6}{5}+3\)

\(\Rightarrow y=\frac{21}{5}\)