$\mu''_{xx}-\mu''_{yy}=f(x,y)$
设 $f(x,y)$, $f'_y(x,y)$ 连续,
\[
\mu(x,y)=\frac{1}{2}\int_{0}^{x}dt\int_{t-x+y}^{-t+x+y}f(t,s)ds
\]
证明:
\[
\mu''_{xx}-\mu''_{yy}=f(x,y).
\]
设 $f(x,y)$, $f'_y(x,y)$ 连续,
\[
\mu(x,y)=\frac{1}{2}\int_{0}^{x}dt\int_{t-x+y}^{-t+x+y}f(t,s)ds
\]
证明:
\[
\mu''_{xx}-\mu''_{yy}=f(x,y).
\]