D={(r,θ)∣4≤r≤5,π2≤θ≤π}D = \bigg\lbrace (r, \theta)|4 \le r \le 5, \frac{\pi}{2} \le \theta \le \pi\bigg\rbraceD={(r,θ)∣4≤r≤5,2π≤θ≤π}