Brudden brøk

$$=\frac{{\displaystyle \frac{2·{\displaystyle \stackrel{3}{\cancel{21}}}}{\cancel{7}}}}{{\displaystyle \frac{5·{\displaystyle \stackrel{7}{\cancel{21}}}}{\cancel{3}}}}=\frac{6}{35}$$

$$=\frac{{\displaystyle \frac{3·12}{4}}+3·12}{5·12-{\displaystyle \frac{2·12}{3}}}=\frac{9+36}{60-8}=\frac{45}{52}$$

$$=\frac{{\displaystyle \frac{7·36}{18}}-1·36-{\displaystyle \frac{1·36}{6}}+{\displaystyle \frac{3·36}{12}}}{{\displaystyle \frac{7·36}{9}}-{\displaystyle \frac{13·36}{4}}}$$

$$=\frac{14-36-6+9}{28-117}=\frac{-19}{-89}=\frac{19}{89}$$

$$=\frac{{\displaystyle \frac{2·\cancel{30}}{\cancel{30}}}-1·30-{\displaystyle \frac{1·{\displaystyle \stackrel{10}{\cancel{30}}}}{\cancel{3}}}+{\displaystyle \frac{2·\stackrel{2}{\cancel{30}}}{\cancel{15}}}}{{\displaystyle \frac{7·\stackrel{5}{\cancel{30}}}{\cancel{6}}}-{\displaystyle \frac{3·\stackrel{6}{\cancel{30}}}{\cancel{5}}}}$$

$$=\frac{2-30-10+4}{35-18}=\frac{-\stackrel{2}{\cancel{34}}}{\cancel{17}}=-2$$

$$=\frac{{\displaystyle \frac{3·\cancel{42}}{\cancel{42}}}+1·42-{\displaystyle \frac{1·{\cancel{42}}^{14}}{\cancel{3}}}}{{\displaystyle \frac{7·{\cancel{42}}^7}{\cancel{6}}}-{\displaystyle \frac{3·{\cancel{42}}^6}{\cancel{7}}}}=\frac{3+42-14}{49-18}=\frac{31}{31}=1$$