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故<br />
∫∫ ( x + y +<br />
Σ<br />
z)<br />
dS<br />
=<br />
2<br />
∫∫<br />
( x<br />
+<br />
y<br />
+<br />
5<br />
−<br />
y)dxdy<br />
D xy<br />
=<br />
2<br />
∫∫ (5 +<br />
x<br />
)dxdy<br />
=<br />
D xy<br />
2π 5<br />
∫ 0 0<br />
2∫ dθ<br />
(5 +<br />
ρ cosθ<br />
) ρ dρ<br />
= 125<br />
2π.