Homework Help: calculus

Posted by H on Sunday, December 25, 2011 at 4:02pm.

The value of c for which f(x) = x + c/x has a local minimum at x= 3 is

(a) -9
(b) - 6
(c) -3
(d) 6
(e) 9

calculus - drwls, Sunday, December 25, 2011 at 7:52pm
df/dx = 1 - c/x^2 = 0
If the minimum is at x = 3, then
c/x^2 = c/9 = 1
c = 9

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