Ta có : 

\(\frac{\frac{2}{5}-\frac{2}{9}+\frac{2}{11}}{\frac{7}{5}-\frac{7}{9}+\frac{7}{11}}-\frac{\frac{1}{3}-\frac{1}{4}+\frac{1}{5}}{\frac{7}{6}-\frac{7}{8}+\frac{7}{10}}\)

\(=\)\(\frac{2\left(\frac{1}{5}-\frac{1}{9}+\frac{1}{11}\right)}{7\left(\frac{1}{5}-\frac{1}{9}+\frac{1}{11}\right)}-\frac{\frac{1}{3}-\frac{1}{4}+\frac{1}{5}}{\frac{7}{2}\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{5}\right)}\)

\(=\)\(\frac{2}{7}-\frac{1}{\frac{7}{2}}\)

\(=\)\(\frac{2}{7}-\frac{2}{7}\)

\(=\)\(0\)

Chúc bạn học tốt ~ 

thank nha

\(\frac{x}{2}=\frac{y}{5}\Rightarrow\frac{x}{6}=\frac{y}{15}\)( 1 )

\(\frac{y}{3}=\frac{5z}{9}\Rightarrow\frac{y}{15}=\frac{z}{9}\)( 2 )

Từ ( 1 ) và ( 2 ) \(\Rightarrow\frac{x}{6}=\frac{y}{15}=\frac{z}{9}\)

Áp dụng tính chất của dãy tỉ số bằng nhau, ta có :

\(\Rightarrow\frac{x}{6}=\frac{y}{15}=\frac{z}{9}=\frac{3x+2y-z}{18+30-9}=\frac{-78}{39}=-2\)

\(\Rightarrow x=-12;y=-30;z=-18\)

\(\frac{x}{2}\)= \(\frac{y}{5}\); \(\frac{y}{3}\)= \(\frac{5z}{9}\)và 3x+2y-z=-78

\(\Rightarrow\)\(\frac{x}{6}\)= \(\frac{y}{15}\); \(\frac{y}{15}\)\(\frac{5z}{45}\) và 3x+2y-z=-78

\(\Rightarrow\)\(\frac{x}{6}\)= \(\frac{y}{15}\)= \(\frac{5z}{45}\) và 3x+2y-z=-78

\(\Rightarrow\)\(\frac{3x}{18}\)= \(\frac{2y}{30}\)= \(\frac{z}{9}\) và 3x+2y-z=-78

Áp dụng tính chất dãy tỉ số bằng nhau ta có:

\(\frac{3x}{18}\)= \(\frac{2y}{30}\)= \(\frac{z}{9}\)= \(\frac{3x+2y-z}{18+30-9}\)= \(\frac{-78}{39}\)= -2

Suy ra:    \(\frac{x}{6}\)= -2 \(\Rightarrow\)x= 6.(-2)=-12

               \(\frac{y}{15}\)= -2 \(\Rightarrow\)y= 15.(-2)=-30

               \(\frac{z}{9}\)= -2 \(\Rightarrow\)z= 9.(-2)=-18

a,- 25/18

b,79/25

làm đầy đủ nhé bn

b) \(\frac{4}{9}x-\frac{1}{2}=\frac{-5}{9}\)

\(\Rightarrow\frac{4}{9}x=\frac{-5}{9}+\frac{1}{2}\)

\(\Rightarrow\frac{4}{9}x=\frac{-1}{18}\)

\(\Rightarrow x=\frac{-1}{18}:\frac{4}{9}\)

\(\Rightarrow x=\frac{-1}{8}\)

a, 11 1/4-(2 5/7+5 1/4)

= 45/4-(19/7+21/4)

= 45/4-223/28

=23/7

b, (8 5/11+3 5/8)-3 5/11

=(93/11+29/8)-38/11

=1063/88-38/11

=69/8

a,  =\(11\frac{1}{4}-2\frac{5}{7}-5\frac{1}{4}\)

\(=\left(11\frac{1}{4}-5\frac{1}{4}\right)-2\frac{5}{7}\)

\(=6-2\frac{5}{7}\)

\(=\frac{23}{7}\)

b,  \(=8\frac{5}{11}+3\frac{5}{8}-3\frac{5}{11}\)

\(=\left(8\frac{5}{11}-3\frac{5}{11}\right)+3\frac{5}{8}\)

\(=5+3\frac{5}{8}\)

\(=\frac{69}{8}\)

\(\frac{5}{3}x-\frac{2}{5}x=\frac{19}{10}\)

\(\left(\frac{5}{3}-\frac{2}{5}\right)x=\frac{19}{10}\)

            \(\frac{19}{15}x=\frac{19}{10}\)

                    \(x=\frac{19}{30}\)

\(\frac{5}{3}x-\frac{2}{5}x=\frac{19}{10}\)

      (5/3 - 2/5)x = 19/10

           19/15x = 19/10

                  x = 19/30