a²+b²+c²+ab+bc-ac
=(1/2)(2a²+2b²+2c²+2ab+2bc-2ac)
=(1/2)(a²+2ab+b²+b²+2bc+c²+a²-2ac+c²)
=(1/2)[(a²+2ab+b²)+(b²+2bc+c²)+(a²-2ac+c²)]
=(1/2)[(a+b)²+(b+c)²+(a-c)²]
=(1/2){(-2013+2010)²+(2010-2014)²+[-2013-(-2014)]²}
=(1/2)[(-3)²+(-4)²+()²]
=(1/2)(9+16+1)
=13
为让楼主看清楚,上边写得比较啰嗦.