抛物线的顶点式如何推导?就是4ac-b2-------怎么推导的了?4a

Question

抛物线的顶点式如何推导?
就是 4ac-b2
-------怎么推导的了?
4a

Answer 1

抛物线是:y=ax^2+bx+c
通过配方得:
y=a(x^2+b/ax+b^2/(4a^2))+c-b^2/(4a)
=a(x+b/2a)^2+(4ac-b^2)/(4a)
所以,顶点坐标是:(-b/2a,(4ac-b^2)/4a)
对称轴是:x=-b/2a