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# Convex functions watch

1. Can a function, f(x), be convex for an interval where f(x) is not defined? I got a question with a function 5x^2 - 6x - ln(x) and it asked for what intervals the function was convex... There were 4 possible answers and all of them included negative values except one of them so I just assumed it had to be that one, am I right?

I looked carefully and it was written ln (x) not ln [x] (modulus)...
2. (Original post by davidsmith)
Can a function, f(x), be convex for an interval where f(x) is not defined? I got a question with a function 5x^2 - 6x - ln(x) and it asked for what intervals the function was convex... There were 4 possible answers and all of them included negative values except one of them so I just assumed it had to be that one, am I right?

I looked carefully and it was written ln (x) not ln [x] (modulus)...
if the function cannot be defined I don't see how it can be convex on an interval it can't be defined on.

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Updated: January 16, 2010
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