x=pcosθ,y=psinθ代入x²＋y²=2x,得
p=2cosθ
即D:
{0≤p≤2cosθ
{-π/2≤θ≤π/2
所以
原式=∫∫f(pcosθ,psinθ)pdpdθ
=∫(-π/2,π/2)dθ∫(0,2cosθ)f(pcosθ,psinθ)pdpdθ