How Do You Calculate Thevenin Equivalents in Circuit Analysis?

[dead_devil_66]

Homework Statement

[PLAIN]http://d.imagehost.org/0018/enunciado.png

It's in portuguese but what it's being asked is to find the Rth and Vth, the Thevenin equivalents for that network, in that cut point...

V2 and all resistors values are known.

Homework Equations

The Attempt at a Solution

For Rth, I'm unsure between

( R2 + R5 ) || ( R4 || R5 )

OR

R2 || ( ( R4 || R3 ) + R5)
For Vth, my solution is using nodal analysis. I guess you guys can see the datum with the 'arrow'.

A: -Ir4 + Ir3 + Ir2 = 0
B: -Ir3 - Ir2 + Ir4 = 0

I'm assuming the positive ones as the currents that go out from the node.

Va = V2
Ir4 = (Vb - Va) / R4
Ir3 = (Va - Vb) / R3
Vth = R2*Ir2 <=> Ir2 = Vth/R2

Vth/R2 = ( Vb - V2 ) / R3 + ( V2 - Vb ) / R4

So, now I'm stuck! How can i get the Vb?
Thanks in advance!

 

[Quinzio]

Break the circuit into 2 pieces then apply Thevenin to part1 then draw the simplified circuita and apply T. again.

It's more intuitive and simple.

 

[dead_devil_66]

and what about using Mesh analysis method?

[PLAIN]http://d.imagehost.org/0269/circuito4.png

J1: -V2 + Vr4 + Vr3 = 0
J2: -Vr3 + Vr5 - Vr2 = 0

J1 is the upper mesh current, J2 is the other one.

By solving the system i got:

J1 = -( ( V2 * ( R5 - R2 - R3 ) ) / ( R3 * ( R5 - R2 + R4 ) ) )

J2 = -( V2 / ( R5 - R2 + R4 ) )

Ir2 = J2


i think that

Vth = Ir2 * R2


Right?

 

[dead_devil_66]

Break the circuit into 2 pieces then apply Thevenin to part1 then draw the simplified circuita and apply T. again.

It's more intuitive and simple.

so, should i sum R2 and R5 and make that sum resistor the load resistor?