5/7-8/13+2/7=5/7+2/7-8/13=1-8/13=5/13(13分之5)不懂可追问|有帮助请采纳。。。
5/7-8/13+2/7=5/7+2/7-8/13=1-8/13=5/13
5/7-8/13+2/7=5/13
=1-8/13=5/13
5/13