右边半圆：x = √(4 - y²)∫∫_D (xy²) dσ= ∫(-2~2) dy ∫(0~√(4 - y²)) xy² dx= ∫(-2~2) x²y²/2 |(0~√(4 - y²)) dy= 2∫(0~2) (4 - y²)y²/2 dy= ∫(0~2) (4y² - y⁴) dy= (4/3)y³ - (1/5)y⁵ |(0~2)= (4/3)(8) - (1/5)(32)= 64/15
