# Help in finding Vout in terms of Vin...

#### Tnyalc

Joined Oct 28, 2013
2
I know that I need to use my voltage divider, but the other resistors are messing me up. Can anyone step me through this one?

#### WBahn

Joined Mar 31, 2012
26,398
You need to first show YOUR best effort to solve YOUR homework problem. Just make the best start that you can. That will let us see how you are approaching things and will let us better guide you toward discovering the key point(s) where you might be having difficulties.

#### Tnyalc

Joined Oct 28, 2013
2
We'll, I know that I will start twill R1+R2. R5/(R4+R5) comes last. And I need to put R3 in parallel. So what I have is :

(1/(1/R3)+(1/(R5/(R4+R5))))+R1+R2

Am I close?

#### WBahn

Joined Mar 31, 2012
26,398
We'll, I know that I will start twill R1+R2. R5/(R4+R5) comes last. And I need to put R3 in parallel. So what I have is :

(1/(1/R3)+(1/(R5/(R4+R5))))+R1+R2

Am I close?
Check the units:

At first glance the units have to be ohms since the last term is +R2. If you want Vout/Vin, you want a voltage divided by a voltage, which is dimensionless. So you KNOW this answer is wrong.

Beyond that

( [1/(1/R3)] + ( 1/([R5/(R4+R5)]) ) ) + [R1+R2]

[1/(1/R3)] has units of resistance (so at least it can be added to R1 and R2).

But [R5/(R4+R5)] is dimensionless, so 1/[..] is dimensionless. This CAN'T be added to the other terms. So even if you were looking for an answer that had units of resistance, this ain't it!

See if this gives you any ideas:

Label the node that connects R2, R3, and R4 as Va.

Q1) If all you had to do was find Va in terms of Vin, could you do it?

Q2) If you knew what Va was, could you find Vout?

• anhnha