diff --git a/Transistor_und_Operationsverstaerker/doc/Hinweise-Kennlinienfeld.md b/Transistor_und_Operationsverstaerker/doc/Hinweise-Kennlinienfeld.md
index 1f15a65959599d96f474e187d87f1376f9926d8b..276c4b2822a4858e85b35ea6f005d8099b242446 100644
--- a/Transistor_und_Operationsverstaerker/doc/Hinweise-Kennlinienfeld.md
+++ b/Transistor_und_Operationsverstaerker/doc/Hinweise-Kennlinienfeld.md
@@ -30,7 +30,7 @@
   &\\
   &U_{\mathrm{BE}} = n\,U_{T}\,\ln\left(\frac{I_{\mathrm{B}}}{I_{S}}+1\right);\\
   &\\
-  &r_{\mathrm{B}} = \frac{\mathrm{d}U_{\mathrm{BE}}}{\mathrm{d}I_{\mathrm{B}}} = n\,\frac{U_{T}}{I_{\mathrm{B}}+1}.
+  &r_{\mathrm{B}} = \frac{\partial U_{\mathrm{BE}}}{\partial I_{\mathrm{B}}} = n\,\frac{U_{T}}{I_{\mathrm{B}}+1}.
   \end{split}
   \end{equation*}
   \end{equation*}