(x-a)²+(x-b)²≥2(x-a)(x-b)(a-x)²+(x-b)²≥-2(a-x)(x-b)a-x+x-b=a-b 为定值当a-x=x-b时 (a-x)²+(x-b)²有最小值x=(a+b)/2(a-x)²+(x-b)²=(a-(a+b)/2)²+(x-(a+b)/2)²= (a-b)²/2
