1) приведите дроби:а) 4/9, 5/6, 7/2 к знаменателю 18;б) 7/8, 5/16, 21/40 к знаменателю...

а) $\frac{4}{9} =\frac{4*2}{18} =\frac{8}{18} \\\\\frac{5}{6} =\frac{5*3}{18} =\frac{15}{18} \\\\\frac{7}{2}= \frac{7*9}{18}= \frac{63}{18}$

б) $\frac{7}{8} =\frac{7*10}{80} =\frac{70}{80} \\\\\frac{5}{16}= \frac{5*5}{80} = \frac{25}{80} \\\\\frac{21}{40}= \frac{21*2}{80}= \frac{42}{80}$

a) $\frac{1*4}{12}= \frac{4}{12}$ и $\frac{1*3}{12} =\frac{3}{12}$

б) $\frac{5*2}{16} =\frac{10}{16}$ и $\frac{3*1}{16}= \frac{3}{16}$

в) $\frac{5*5}{40}= \frac{25}{40}$ и $\frac{3*2}{40}= \frac{6}{40}$

г) $\frac{2*8}{72}= \frac{16}{72}$ и $\frac{7*3}{72}= \frac{21}{72}$