(4又12分之5-1又7分之3)-(1又7分之4-1又12分之7)= ( 4 +5/12 - 1 - 3/7 ) - ( 1 + 4/7 - 1- 7/12)= ( 3+5/12 - 3/7 ) - ( 4/7 - 7/12)= 3+5/12 - 3/7 - 4/7 +7/12= 3 - (3/7 + 4/7) +7/12 +5/12= 3 -1 + 1= 3无量寿...