若X/Y=7/5,则Y-X/X+3Y=

问题描述:

若X/Y=7/5,则Y-X/X+3Y=

X/Y=7/5,
设x=7a,y=5a,代入后式得到:
Y-X/X+3Y
=(5a-7a)/(7a+15a)
=-2a/22a
=-1/11.