∫∫(a-√(x^2+y^2))dxdy
用极坐标
=∫∫(a-r)r drdθ
=∫[0--->2π]dθ ∫[0--->a] (ar-r²) dr
=2π∫[0--->a] (ar-r²) dr
=2π[(a/2)r²-(1/3)r³] |[0--->a]
=πa³/3
∫∫(a-√(x^2+y^2))dxdy
用极坐标
=∫∫(a-r)r drdθ
=∫[0--->2π]dθ ∫[0--->a] (ar-r²) dr
=2π∫[0--->a] (ar-r²) dr
=2π[(a/2)r²-(1/3)r³] |[0--->a]
=πa³/3