$\frac{a}{b}\div\frac{c}{d}$

$\frac{a}{b}\times\frac{c}{d}$

$\frac{a}{b}=\frac{c}{d}$

$\frac{10}{19}$

$\frac{15}{7}$

$\frac{3}{4}$

$bc$

$ab$

$ac$

$\frac{c}{d}$

$\frac{a}{d}$

$\frac{d}{c}$

$\frac{6}{11}$

$\frac{15}{26}$

$\frac{3}{5}$

$\frac{x^2+2}{3}$

$\frac{x^2+2x}{3}$

$\frac{x^2+1}{3}$

$\frac{8}{21}$

$\frac{10}{3}$

$\frac{4}{9}$

$\frac{2\left(a-1\right)}{3\left(a+1\right)}$

$\frac{\left(a-1\right)}{3\left(a+1\right)}$

$\frac{2\left(a-1\right)}{\left(a+1\right)}$

$\frac{6}{11}$

$\frac{5}{6}$

$\frac{3}{5}$

$\frac{3}{4}$

$\frac{2}{4}$

$\frac{\frac{4}{5}}{\frac{1}{2}}$

5