f(x)=x(x-a)(x-b)点A（s,f(s)）,B（t,f(t)）.若0

向量OA*向量OB=st+st(s^2-(a+b)s+ab)(t^2-(a+b)t+ab)①f'(x)=3x^2-2(a+b)x+ab=0韦达定理得s+t=2(a+b)/3=4/√3②（代入a+b=2√3)st=ab/3③把②③代入①得向量OA*向量OB=st+((st)^2)*(s+t-4/√3+2t)(t+s-4/√3+2s）④...