I want to find the the supremum of $\dfrac{|x|^{2/3}-|y|^{2/3}}{|x-y|^{2/3}} $ in the unit ball centered at the origin . Here $x\neq y$, $x,y \in \mathbb R^n$. How do I proceed ? Thank you for your help.
Finding $\sup$ of the given function in Ball of radius $1$ centered at origin.
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multivariable-calculus
1 Answers
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Hint: By a modification of the triangular inequality you see that $$||x|^{2/3}-|y|^{2/3}|\leq |x-y|^{2/3}$$ for all $x\neq y$. So we have$$\dfrac{|x|^{2/3}-|y|^{2/3}}{|x-y|^{2/3}}\leq 1$$ Is the value of the function $=1$ at some point?
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0Yup at $x=0, y=1$ . – 2012-07-13
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0So does this answer your question? – 2012-07-13
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0@SimonMarkett : Yup :) . thanks a ton . – 2012-07-13
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0Btw it's $x=1$, $y=0$. @did I had to look up maieutics...but thx ;) – 2012-07-13