\[h_{\text{ib}}=\frac{\text{h}_{\text{ie}}}{1+\text{h}_{\text{fe}}}\]
\[h_{\text{ib}}=\frac{h_{\text{ie}} h_{\text{oe}}}{1+h_{\text{fe}}}-h_{\text{re}}\]
\[h_{\text{fb}}=\frac{-\text{h}_{\text{fe}}}{1+\text{h}_{\text{fe}}}\]
\[h_{o b}=\frac{h_{o e}}{1+h_{f e}}\]