\(a)\text{ Ta có }\frac{2}{3}=\frac{8}{12};\text{ }\frac{1}{4}=\frac{3}{12}\) 

\(\frac{8}{12}>\frac{3}{12}\)\(\Rightarrow\frac{2}{3}>\frac{1}{4}\)

\(b)\text{ Ta có }10>8\)

\(\Rightarrow\frac{7}{10}< \frac{7}{8}\)

\(c)\text{Ta có }\frac{3}{5}=\frac{6}{10}\)

\(\text{mà }7< 10\)

\(\Rightarrow\frac{6}{7}>\frac{6}{10}\)

\(\Rightarrow\frac{6}{7}>\frac{3}{5}\)

cho mình hỏi "va"là gì zợ

\(\frac{2}{5}\cdot5\frac{1}{4}-\frac{2}{7}\cdot3\frac{1}{4}\)

= \(\frac{2}{5}\cdot\frac{21}{4}-\frac{2}{7}\cdot\frac{13}{4}\)

= \(\frac{21}{10}-\frac{13}{14}\)

= \(\frac{41}{35}\)

\(\left(2\frac{1}{3}+3\frac{1}{2}\right):\left(-4\frac{1}{6}+3\frac{1}{7}\right)+7\frac{1}{2}\)

= \(\left(\frac{7}{3}+\frac{7}{2}\right):\left(\frac{-25}{6}+\frac{22}{7}\right)+\frac{15}{2}\)

= \(\frac{35}{6}:\frac{-43}{42}+\frac{15}{2}\)

= \(\frac{-245}{43}+\frac{15}{2}\)

= \(\frac{155}{86}\)

có phải như ngọc nguyễn minh nói không vậy?