9.1.4 Double integrals
Problem:
Calculate the mass of the plate \( D \) with density, where
\[
\mu=\frac{2 y-3 x}{x^{2}+y^{2}}, \quad D:\left\{\begin{array}{l}
x^{2}+y^{2}=4 \\
x^{2}+y^{2}=16 \\
x=0, y=0,(x \leq 0, y \geq 0)
\end{array}\right.
\]