# Differentiating the following average.

I am trying to find $\frac{\partial ^2}{\partial r^2} \frac{1}{|\partial B(x,r)|} \int_{\partial B(x,r)} u(y,t)\mathrm{d}y$ . Where $B$ is a ball of radius $r$ with center at $x$ .

Differentiating once was ok , but i couldn't not again differentiate .

Thank you for your help .

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What's "average" doing in there? –  joriki Jul 10 '12 at 10:40
@joriki : I don't know how to make it $\int$ with the cut , ie average of surface integral . –  Theorem Jul 10 '12 at 10:42
AFAIK the \strokedint or \fint commands are not implemented in MathJax, so I just replaced it by the definition. –  Willie Wong Jul 10 '12 at 11:02
@WillieWong : Thank you . –  Theorem Jul 10 '12 at 11:06