1dia

2+5+7+12=262\cdot5+7=17
\frac{1}{4}+\frac{2}{3}=\frac{3}{12}+\frac{8}{12}=\frac{11}{12}
\frac{1}{4}\cdot\frac{2}{3}=\frac{1\cdot2}{4\cdot3}=\frac{2}{12}=\frac{1}{6}
\frac{1}{4}:\frac{2}{3}=\frac{1}{4}\cdot\frac{3}{2}=\frac{3}{8}
\left(\frac{2}{3}\right)^2=\frac{2^2}{3^2}=\frac{4}{9}