已知二次函数y=ax^+bx+c的图象过A(t1,y1) B(t2,y2) 两点且满足a^+(y1+y2)a+y1y2=0<1>证明 y1=-a或y2=-a<２>证明b^-4ac>0 (a不等于0)<３>若函数y的图象与x轴的焦点为M(x1,0) N(x2,0)且x1<x2证明x1<t1<x2 , x1<t2<x2