a-b=3+2√2,b-c=3-2√2
相加
a-c=6
原式=(2a²+2b²+2c²-2ab-2bc-2ac)/2
=[(a²-2ab+b²)+(b²-2bc+c²)+(c²-2ac+a²)]/2
=[(a-b)²+(b-c)²+(a-c)²]/2
=(17+12√2+17-12√2+36)/2
=35