for only emitterresiatance circuit,
voltage gain=collector resistance/emitter resistance
for emitter resistance along with capacitor,
Volt.gain=transconductancex collector resistance
actual expression for voltage gain is
( transconductance x collector resistance)/(1+transconductance x emit.resistance)
for the first case it will become " collector resistance/emitter resistance" since
(1<<<<transconductance x emit. resistance)
for the second case emit .resitance will be surpassed by capacitance ,so it will become as i mentioned above