Question

二次函数解析式最值:-b/2a,(4ac-b^2;)/4a)怎么推导出来的?

Answer 1

y=ax²+bx+c(a≠0)

=a(x²+bx/a)+c

=a(x²+bx/a+b²/4a²-b²/4a²)+c

=a(x+b/2a)²-b²/4a+c

=a(x+b/2a)²+(4ac-b²)/4a

当x=-b/2a时,y=(4ac-b²)/4a