Describe the surface dened by 1 ≤ r ≤ 2, 0◦ ≤ θ ≤ 90◦.
Here r varies from 1 to 2 and θ varies from 0◦ to 90◦. Figure 4.18 illustrates the surface so formed.
\text { At } \mathrm{P}, r=1, \theta=0^{\circ} \text {; at } \mathrm{Q}, r=2, \theta=0^{\circ} \text {; at } \mathrm{R}, r=1, \theta=90^{\circ} \text {; at } \mathrm{S}, r=2, \theta=90^{\circ} \text {. }