在极坐标中，D={(r,θ)|1≤r≤3,π/6≤θ≤π/3}原式=∫(π/6,π/3)dθ∫(1,3)θrdr=[∫(π/6,π/3)θdθ][∫(1,3)rdr]=(1/2)θ^2|(π/6,π/3)(1/2)r^2|(1,3)=(1/4)(π^2/9-π^2/36)(9-1)=π^2/6
