a-b=4,b-c=3
两式相加得：a-c=7
(a-b)²+(b-c)²+(a-c)²=2a²+2b²+2c²-2ab-2bc-2ac
即：16+9+49=2a²+2b²+2c²-2ab-2bc-2ac
74=2a²+2b²+2c²-2ab-2bc-2ac
所以,a²+b²+c²-ab-bc-ac=37