Maths

2009-11-06 4:34 am
Let f(x) = x^2 + 2x - 2 and g(x)= -2x^2 - 12x - 23, where g(x)<0.
Find the greatest and least values of f(x)/g(x).
更新1:

where g(x)<0 for all real values of x.

回答 (1)

2009-11-06 5:07 am
✔ 最佳答案
Let y = f(x)/g(x) = (x^2 + 2x - 2) / (-2x^2 - 12x - 23)
y(-2x^2 - 12x - 23) = x^2 + 2x - 2
(1 + 2y)x^2 + (2 + 12y)x + (23y - 2) = 0
For real x, discriminant >= 0
(2 + 12y)^2 - 4(1 + 2y)(23y - 2) >= 0
4 + 48y + 144y^2 - 4(46y^2 + 19y - 2) >= 0
4 + 48y + 144y^2 - 184y^2 - 76y + 8 >= 0
-40y^2 - 28y + 12 >= 0
10y^2 + 7y - 3 <= 0
(10y - 3)(y + 1) <= 0
-1 <= y <= 0.3
The greatest value is 0.3, the smallest value is -1


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