# Re: minimising and maximising

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Posted by KK on August 28, 2002 at 01:52:43:

In Reply to: Flashlight -- I like that analogy... (n/t) posted by Subhotosh Khan on August 27, 2002 at 12:09:47:

: : :But how does it prove that the equation
: : : y=(2000+20x+10x^1/2)/x cannot be minimised (i.e. the function does not have a convex). I thought we have to take the second derivative because for a convex to occur f"(x)>0.

: : Please listen carefully, KK.

: : The function had NO critical values.
: : (We set the first derivative equal to 0
: : and could not solve for x.)
: : Therefore, there are NO maximums or minimums.

: : Why do we take the second derivative?
: : To test the Critical Values for max or min.
: : But there are NO critical values to test.

: : [Your flashlight doesn't work. I tell you that
: : there are no batteries in it. And you insist on
: : trying a battery-tester?]

Hi, sorry I know that I'm quite slow at maths, but I have tried drawing the graph on Microsoft excel. I got a graph with no miniums :) .. but the graph shows that at zero, it is undefined. I.e. When x=0.009 the corresponding y was a huge number.
It falls and falls but never increase again. Is that part counted as maximising ? IF it is a maximising part, then how come there's no critical value for it?

Thank you so much for your help. I really appreciate it because uI have gained so much more understanding by asking those questions.. Thank you for your time.

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