原式=(1/2)(a²-2ab+b²+a²-2ac+c²+b²-2bc+c²) =(1/2)((a-b)²+(a-c)²+(b-c)²) =(1/2)((2001x+2002-2001x-2003)²+(2001x+2002-2001x-2004)²+(2001x+2003-2001x-2004)²) =(1/2)*((-1)²+(-2)²+(-1)²) =(1/2)*(1+4+1) =3
