a+x²-(b+x)²=a-b=-1
同理
b-c=-1
c-a=2
原式=(c²+b²+a²-ab-bc-ca)/abc
=(2a²+2b²+2c²-2ab-2bc-2ac)/2abc
=[(a²-2ab+b²)+(b²-2bc+c²)+(c²-2ac+a²)]/2abc
=[(a-b)²+(b-c)²+(c-a)²]/2abc
=(1+1+4)/(2×24)
=1/8