The input and output characteristics, of a n-p-n transistor, in its CE configuration, are as
shown.


Input resistance

${\mathrm{r}}_{\mathrm{i}}={\left(\frac{{\mathrm{\Delta V}}_{\mathrm{BE}}}{{\mathrm{\Delta I}}_{\mathrm{B}}}\right)}_{{\mathrm{V}}_{\mathrm{CE}}}$

The relevant values can be read from the input characteristics.
Current amplification factor
$\mathrm{\beta }={\mathrm{\Delta I}}_{\mathrm{C}}/{\mathrm{\Delta I}}_{\mathrm{B}}$

The relevant values can be read from the output characteristics,
corresponding to a given value of 𝑉_𝑪𝑬.