# Single Transistor Overall Current Gain

hisotaso

## Homework Statement

THe problem statement and given solutions are in this thread:

I do not understand the equation for current gain:

## Homework Equations

Ai = $\alpha$$\frac{R4}{R4 + Ri}$

## The Attempt at a Solution

I have pages of work on this, but basically what I know is $\frac{Io}{Ie}$ = $\alpha$

then $\frac{Ie}{Ii}$ must equal $\frac{R4}{R4 + Ri}$, I don't see that.