25-5/12-7/18
=25-15/36-14/36
=25-(15/36+14/36)
=25-29/36
=24+7/36 (24又7/36)��3����21��֮9��14��֮9���أ�ͬ������ʽ���㣬лл��3-(9/21-9/14)=3-(18/42-27/42)=3-( - 9/42)=3+3/14