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