[(1i1/2)do kwadratu-1i3/5;1i1/3];21=PROSZĘ!
źródło:
[(1\frac{1}{2})^2-1\frac{3}{5}:1\frac{1}{3}]:21=[(\frac{3}{2})^2-\frac{8}{5}*\frac{3}{4}]:21=
=[\frac{9}{4}-\frac{6}{5}]:21=[\frac{45}{20}-\frac{24}{20}]:21=\frac{21}{20}*\frac{1}{21}=\frac{1}{20}