Question

在平面直角坐标系xOy中,已知二次函数y=ax2+bx+c(a≠0)的图象与x轴交于A,B两点(点A在点B的左边）,

Answer 1

y(2) = 4a + 2b + c = 3

y(-3) = 9a - 3b + c = -12

y(0) = y(2) = c = 3

所以 a = -1,b = 2

y = -x^2 + 2 x + 3 = -(x-1)^2 + 4

A(-1,0),B(3,0),C(0,3)

AC斜率为3,

k = 3,y = 3x 与BC交于D(3/4,9/4),ABC 与OBD相似

P点横坐标 为Px

当 1 < Px < 5,PCO > ACO

当Px > 5,PCO < ACO