Question

已知二次函数y=f(x)中,f(1)=f(-5)=0,顶点坐标为9/2

Answer 1

由已知,1,-5为两个根,故可设y=a(x-1)(x+5)=a(x^2+4x-5)=a(x+2)^2-9a

顶点纵坐标=-9a=9/2,得：a=-1/2

所以f(x)=-(x+2)^2/2+9/2

2)对称轴为x=-2

因此当x