Câu 1:  \(\frac{5}{7}\):x+\(\frac{2}{3}\)=1\(\frac{1}{3}\)

\(\frac{5}{7}\):x+\(\frac{2}{3}\)=\(\frac{4}{3}\)

\(\frac{5}{7}\):x=\(\frac{4}{3}\)  -    \(\frac{2}{3}\)

\(\frac{5}{7}\):x=\(\frac{2}{3}\)

x=\(\frac{5}{7}\):\(\frac{2}{3}\)

x=\(\frac{15}{14}\)

Câu 2:x*\(\frac{3}{7}\)-\(\frac{5}{14}\)=2\(\frac{1}{3}\)

x*\(\frac{3}{7}\)-\(\frac{5}{14}\)=\(\frac{7}{3}\)

x*\(\frac{3}{7}\)=\(\frac{7}{3}\)+\(\frac{5}{14}\)

x*\(\frac{3}{7}\)=\(\frac{113}{42}\)

x=\(\frac{113}{42}\):\(\frac{3}{7}\)

x=\(\frac{791}{126}\)

Câu 3:  3\(\frac{5}{7}\)-x*\(\frac{1}{3}\)=1\(\frac{13}{11}\)

\(\frac{26}{7}\)-x*\(\frac{1}{3}\)=\(\frac{24}{11}\)

x*\(\frac{1}{3}\)=\(\frac{26}{7}\)-\(\frac{24}{11}\)

x*\(\frac{1}{3}\)=\(\frac{118}{77}\)

x=\(\frac{118}{77}\):\(\frac{1}{3}\)

x=\(\frac{356}{77}\)

\(a,\frac{1}{2}x+\frac{3}{5}\left(x-2\right)=3\)

\(\Rightarrow\frac{1}{2}x+\frac{3}{5}x-\frac{6}{5}=3\)

\(\Rightarrow x\left(\frac{1}{2}+\frac{3}{5}\right)=3+\frac{6}{5}\)

\(\Rightarrow\frac{11}{10}x=\frac{21}{5}\)

\(\Rightarrow x=\frac{21}{5}:\frac{11}{10}\)

\(\Rightarrow x=\frac{42}{11}\)

\(b,\left(3\frac{1}{2}-x\right).1\frac{1}{4}=-1\frac{1}{20}\)

\(\Rightarrow\left(\frac{7}{2}-x\right)\cdot\frac{5}{4}=-\frac{21}{20}\)

\(\Rightarrow\frac{7}{2}-x=-\frac{21}{20}:\frac{5}{4}\)

\(\Rightarrow\frac{7}{2}-x=-\frac{21}{25}\)

\(\Rightarrow x=\frac{7}{2}--\frac{21}{25}\)

\(\Rightarrow x=\frac{7}{2}+\frac{21}{25}\)

\(\Rightarrow x=\frac{217}{50}\)

a) \(\frac{1}{2}.x+\frac{3}{5}.\left(x-2\right)=3\)

    \(\frac{1}{2}.x+\frac{3}{5}.x-2=3\)
    \(\frac{1}{2}.x+\frac{3}{5}.x=3+2\)
    \(\frac{1}{2}.x+\frac{3}{5}.x=5\)
    \(x.\left(\frac{1}{2}+\frac{3}{5}\right)=5\)
    \(x.\frac{11}{10}=5\)
    \(x=\frac{50}{11}\)
b) \(\left(3\frac{1}{2}-x\right).1\frac{1}{4}=-1\frac{1}{20}\)
               \(\left(7-x\right).5=-21\)
                   \(\left(7-x\right)=-21:5\)
                         \(7-x=-4,2\)
                                  \(x=7-\left(-4,2\right)\)
                                  \(x=11,2\)

[3,8 : (x + 1,05)] : \(\frac{1}{3}\)= 2\(\frac{1}{9}\)

\(\left[\frac{19}{5}:\left(x+\frac{21}{20}\right)\right]:\frac{1}{3}=\frac{19}{9}\)

\(\frac{19}{5}:\left(x+\frac{21}{20}\right)=\frac{19}{9}.\frac{1}{3}=\frac{19}{27}\)

\(x+\frac{21}{20}=\frac{19}{5}:\frac{19}{27}=\frac{27}{5}\)

\(x=\frac{27}{5}-\frac{21}{20}\)

\(x=\frac{87}{20}\)

Theo đề:  \(2x+y=0\Leftrightarrow y=-2x\)    \(\left(1\right)\)

Ta có:   

\(\dfrac{3-x}{y-4}=\dfrac{2}{5}\)

\(\Leftrightarrow5\left(3-x\right)=2\left(y-4\right)\)

\(\Leftrightarrow15-5x=2y-8\)

\(\Leftrightarrow15+8=2y+5x\)

\(\Leftrightarrow5x+2y=23\)    \(\left(2\right)\)

Thế (1) vào (2), suy ra:

    \(5x+2.\left(-2x\right)=23\)

\(\Leftrightarrow5x-4x=23\)

\(\Leftrightarrow x=23\)

\(\Rightarrow y=-2.23=-46\)

\(a,x-\frac{5}{6}:1\frac{1}{6}=0,125\)

\(x-\frac{5}{6}:\frac{7}{6}=\frac{1}{8}\)

\(x-\frac{5}{7}=\frac{1}{8}\)

\(x=\frac{1}{8}+\frac{5}{7}\) \(x=\frac{47}{56}\)

\(b,\left(1-\frac{2}{10}+x+\frac{1}{5}\right):\left(1\frac{1}{3}-\frac{2}{3}+3\frac{1}{3}\right)-1=1\frac{1}{2}\)

\(\left(1-\frac{1}{5}+x+\frac{1}{5}\right):\left(\frac{4}{3}-\frac{2}{3}+\frac{10}{3}\right)-1=\frac{3}{2}\)

\(\left(\frac{4}{5}+x+\frac{1}{5}\right):4=\frac{3}{2}+1\)

\(\left(1+x\right):4=\frac{5}{2}\)

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

\(1+x=10\)

\(x=10-1\)

\(x=9\)

BÀI 1:

         \(541-\left(125-x\right)\times2\frac{2}{3}=469\)

        \(\Rightarrow541-\left(125-x\right)\times\frac{8}{3}=469\)

         \(\Rightarrow541-\frac{1000}{3}+\frac{8}{3}\times x=469\)

          \(\Rightarrow\frac{623}{3}-\frac{8}{3}\times x=469\)

          \(\Rightarrow\frac{8}{3}\times x=\frac{784}{3}\)

           \(\Rightarrow x=98\)

BÀI 2 : 

       \(A=\frac{1}{2\times3}+\frac{1}{2\times3\times4}+\frac{1}{3\times4\times5}+...\)\(+\frac{1}{18\times19\times20}\)

            \(=\frac{1}{2}\times\left(\frac{1}{1\times2}+\frac{1}{2\times3}\right)+\frac{1}{2}\times\left(\frac{1}{2\times3}+\frac{1}{3\times4}\right)\)\(+...+\frac{1}{2}\times\left(\frac{1}{18\times19}+\frac{1}{19\times20}\right)\)

             \(=\frac{1}{2}\times\left(\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{2\times3}+...+\frac{1}{19\times20}\right)\)

               \(=\frac{1}{2}\times\left(\frac{1}{1\times2}-\frac{1}{19\times20}\right)\)

                \(=\frac{1}{2}\times\frac{189}{380}\)

                  \(=\frac{189}{760}\)

ĐÃ ĐÁP ỨNG THỈNH CẦU

😃😃😃

cau b ta co9;(x+x+.....+x)-(1+2+....+100)=4950

                   100x           -  5050              =4950

                               100x                        =4950+5050

                                       100x                   =10000

                                              x=10000 ;100

                                              x=100