Question

Решите пожалуйста срочно. 1 тур, 1;3;5 строки

Answer 1

1 строка  →

$\displaystyle\\\frac{2}{5} -\frac{1}{20}=\frac{2*4}{5*4}-\frac{1}{20}=\frac{8}{20}-\frac{1}{20}=\frac{7}{20}\\\\\\\frac{17}{18}-\frac{1}{2}=\frac{17}{18}-\frac{1*9}{2*9}=\frac{17}{18}-\frac{9}{18}=\frac{8}{18}=\frac{4}{9} \\\\\\\frac{6}{7}-\frac{2}{5}=\frac{6*5}{7*5}-\frac{2*7}{5*7}=\frac{30}{35}-\frac{14}{35}=\frac{16}{35}$

3 строка  →

$\displaystyle\\\frac{5}{12}-\frac{1}{3}=\frac{5}{12}-\frac{1*4}{3*4}=\frac{5}{12}-\frac{4}{12}=\frac{1}{12} \\\\\\\frac{2}{3}-\frac{4}{9}=\frac{2*3}{3*3}-\frac{4}{9}=\frac{6}{9}-\frac{4}{9}=\frac{2}{9}\\\\\\\frac{13}{15}-\frac{5}{6}=\frac{13*2}{15*2}-\frac{5*5}{6*5}=\frac{26}{30}-\frac{25}{30}=\frac{1}{30}$

5 строка  →

$\displaystyle\\\frac{4}{5}-\frac{8}{15}=\frac{4*3}{5*3}-\frac{8}{15}=\frac{12}{15}-\frac{8}{15}=\frac{4}{15}\\\\\\\frac{4}{5}-\frac{2}{13}=\frac{4*13}{5*13}-\frac{2*5}{13*5}=\frac{52}{65}-\frac{10}{65} =\frac{42}{65}\\\\\\\frac{6}{7}-\frac{3}{4}=\frac{6*4}{7*4}-\frac{3*7}{4*7}=\frac{24}{28}-\frac{21}{28}=\frac{3}{28}$