Công thức 1: (a + b). c = a.b + b.c
Áp dụng: $\left(\frac{1}{2}+\frac{3}{4}\right).\frac{2}{3}$
$=\frac{1}{2}.\frac{2}{3}+\frac{3}{4}.\frac{2}{3}=\frac{1}{3}+\frac{1}{2}$
$=\frac{2}{6}+\frac{3}{6}=\frac{5}{6}$
Công thức 2: $\frac{\left(a+b\right).c}{-\left(d+e\right)}$
Áp dụng $\frac{\left(\frac{1}{2}+\frac{3}{4}\right).\frac{2}{5}}{-\left(\frac{5}{2}+\frac{1}{3}\right)}=\frac{\left(\frac{2}{4}+\frac{3}{4}\right).\frac{2}{5}}{-\left(\frac{15}{6}+\frac{2}{6}\right)}=\frac{\frac{5}{4}.\frac{2}{5}}{-\frac{17}{6}}=\frac{\frac{1}{2}}{-\frac{17}{6}}=\frac{1}{2}.\frac{-6}{17}=\frac{-3}{17}$