First Order Transient: RC Circuit

[jclay06]

Homework Statement

http://i.thespiffylife.com/files/1/trans1.jpg

i have to find Vc(t)

Homework Equations

I know that Vc(0+) = Vc(0) = Vc(0-) and Vc = Vs*e^(-t/RC)

The Attempt at a Solution

What I'm unsure on is what the equivalent resistance of the circuit would be so I could find the time constant. I know since the Capacitor is fully charged it now behaves as a voltage source, but for any nodal / mesh equation I come up with I'm always one equation short of having equal unknowns & equations.
So ... any help on how to find the Req would be nice.

 

[MATLABdude]

Homework Statement

http://i.thespiffylife.com/files/1/trans1.jpg

i have to find Vc(t)

Homework Equations

I know that Vc(0+) = Vc(0) = Vc(0-) and Vc = Vs*e^(-t/RC)

The Attempt at a Solution

What I'm unsure on is what the equivalent resistance of the circuit would be so I could find the time constant. I know since the Capacitor is fully charged it now behaves as a voltage source, but for any nodal / mesh equation I come up with I'm always one equation short of having equal unknowns & equations.
So ... any help on how to find the Req would be nice.

Find the Thévenin equivalent around the capacitor.

EDIT: Before, or after t=0? Which will affect the time constant?