標題: f4數學不會f4 [打印本頁]

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作者: 食音食字    時間: 2009-2-22 22:19     標題: f4數學不會f4

若兩個數之和是16,求它們的積的極大值

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作者: 唔係四川    時間: 2009-2-23 15:11

x+y=16
y=16-x

Product = xy = x(16-x) = 16x-x^2.  Rewriting in the form ax^2+bx+c gives a=-1, b=16.

Turning point is at (-b/2a, f(-b/2a)) = (8, 64).  Checking that it is a maximum, the answer is 64.

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