Let a quadratic function y=f(x). If the coordinates of the vertex of the graph are (3,15), and the graph touches at one point (0,-2) at x-axis. Then f(x) =?
The answer is -3/5 (x+2)(x-8). How is the explanation?
更新1:
係ar...唔好意思, 打錯左, 應該係(-2,0)
中四數學問題 (Quadratic Function)
2013-06-08 5:39 pm
MC Question:
Let a quadratic function y=f(x). If the coordinates of the vertex of the graph are (3,15), and the graph touches at one point (0,-2) at x-axis. Then f(x) =?
The answer is -3/5 (x+2)(x-8). How is the explanation?
Let a quadratic function y=f(x). If the coordinates of the vertex of the graph are (3,15), and the graph touches at one point (0,-2) at x-axis. Then f(x) =?
The answer is -3/5 (x+2)(x-8). How is the explanation?
回答 (2)
2013-06-08 6:08 pm
✔ 最佳答案
Since the coordinates of the vertex of the graph are (3,15),y = f(x)= a(x-3)^2+15
The statement of "the graph touches at one point (0,-2) at x-axis" is wrong. At (0,2), the point is on y-axis since the x-coordinate is 0. But the y-coordinate is non-zero. Therefore the point is not on x-axis.
If the correct statement is "the graph touches at one point (0,-2) at y-axis",
When x=-2, y=0
0 = a(-2-3)^2+15
a = -3/5
Therefore the model answer of f(x) = -3/5*(x-3)^2+15 = -3/5*(x+2)(x-8) is obtained.
2013-06-08 12:17:12 補充：
The correct statement is "the graph touches at one point (-2,0) at x-axis"
2013-06-08 7:24 pm
The question should reads "the graph cuts the x-axis at (-2,0)"
收錄日期: 2021-04-24 10:15:03
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20130608000051KK00047