a-b=2+根号3，b-c=2-根号3两式相加得：a-c=4则：a²+b²+c²-ab-ac-bc=(1/2)(2a²+2b²+2c²-2ab-2ac-2bc)=(1/2)[(a-b)²+(b-c)²+(a-c)²]=(1/2)*[(2+√3)²+(2-√3)²+4²]=(1/2)*(7+7+16)=15
15
