∵xy/(a+b)=1/15
∴a+b=15xy
同理:
b+c=17xy
a+c=16xy
∴xy/(a+b+c)
=xy/[1/2(2a+2b+2c)]
=xy/[1/2(a+b+b+c+a+c)]
=xy/[1/2(15xy+17xy+16xy)]
=xy/[1/2×48xy]
=xy/(24xy)
=1/24
∵xy/(a+b)=1/15
∴a+b=15xy
同理:
b+c=17xy
a+c=16xy
∴xy/(a+b+c)
=xy/[1/2(2a+2b+2c)]
=xy/[1/2(a+b+b+c+a+c)]
=xy/[1/2(15xy+17xy+16xy)]
=xy/[1/2×48xy]
=xy/(24xy)
=1/24