Hello,

Here is what I've done.

I'm finding two extreme values : and (so the first one is a maximum and the second one a minimum), each of them attained at two points.

Sorry for the writing, I've got a problem with writing on a straight line

I hope it looks correct and helps you.

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Note that your answers for min and max yield the same result for f.

Since it is a symmetric function, f((-sqrt(13/8),0,0))=f((sqrt(13/8),0,0))