>>485
>(x-7)(x-9)+(x-9)(x-11)+(x-11)(x-7)=0 の２解をa,bとするとき

(a-7)(a-9)+(a-9)(a-11)+(a-11)(a-7)=(b-7)(b-9)+(b-9)(b-11)+(b-11)(b-7)=0だが
(a-7)(b-9)+(a-9)(b-11)+(a-11)(b-7)=-8≠0