Whakaoti i te pi*9^2*80/360=

$$\pi \times { 9 }^{ 2 } \times \frac{ 80 }{ 360 } =$$

Aromātai

$$18\pi \approx 56.548667765$$

Ngā Upane Otinga

Tātaihia te 9 mā te pū o 2, kia riro ko 81.

$$\pi \times 81\times \frac{80}{360}$$

Whakahekea te hautanga \frac{80}{360} ki ōna wāhi pāpaku rawa mā te tango me te whakakore i te 40.

$$\pi \times 81\times \frac{2}{9}$$

Tuhia te 81\times \frac{2}{9} hei hautanga kotahi.

$$\pi \times \frac{81\times 2}{9}$$

Whakareatia te 81 ki te 2, ka 162.

$$\pi \times \frac{162}{9}$$

Whakawehea te 162 ki te 9, kia riro ko 18.

$$\pi \times 18$$