中四a.mth
2007-10-29 3:13 am
the vertex of the parabola is on the line y=20,the y-intecept is 15,and one of the x-intercept is 3 (2 possibilities).
回答 (2)
2007-10-29 3:31 am
✔ 最佳答案
set y=a(x-h)^2+20when (x,y)=(0,15)
ah^2=-5-----(1)
when (x,y)=(3,0)
a(3-h)^2=-20-------(2)
(2),
(-5/h^2)(9-6h+h^2)=-20
-45+30h-5h^2=-20h^2
15h^2+30h-45=0
h=-3 or h=1
when h=-3 a=-5/9
when h=1 a=-5
the parabola formular :y=-5/9(x+3)+20 or y=-5(x-1)^2+20
2007-10-29 3:20 am
20-15-3=2
收錄日期: 2021-04-13 18:44:38
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20071028000051KK04186