?$\frac {1}{3} \div a=\frac {1}{3} ×\frac {1}{a}=\frac {1}{3\ \mathrm {a}}$?
?$\frac {1}{a} \div 3=\frac {1}{a} ×\frac {1}{3}=\frac {1}{3\ \mathrm {a}}$?
發(fā)現(xiàn)：?$\frac {1}{3} \div a=\frac {1}{a} \div 3$?
將?$ a=2 $?代入檢驗得，
?$\frac {1}{3} \div a=\frac {1}{3} \div 2=\frac {1}{6}$?，?$\frac {1}{a} \div 3=\frac {1}{2} \div 3=\frac {1}{6}$?。
