\[P=\frac{\pi}{4} \times d^{2} \times \sigma_{t}\]
\[P=2 \frac{\pi}{4}\left(d_{2}\right)^{2} \tau\]
\[P=\left(d_{2}-d_{1}\right) t \times \sigma_{t}\]
\[P=\left(d_{2}-d_{1}\right) t \times \tau\]
\[P=\left(d_{2}-d_{1}\right) 2 t_{1} \times \sigma_{t}\]
\[P=d_{1} \times 2 t_{1} \times \sigma_{c}\]