**Here is an example of an op amp used for amplification:**

[![enter image description here](https://i.stack.imgur.com/3tRi3.png)](https://i.stack.imgur.com/3tRi3.png)

**What I understand:**

* C1 is used as AC coupling to remove any DC bias.
* Vref is used to apply a DC voltage to be able to amplify negative voltage values.
* R2 and R1 these are used for gain.
* C2 is used such that the gain formed by R2 and R1 only apply to AC signals as C2 at low frequencies looks like open circuit for DC

**What I think I understand:**

* Since there is no input current, ideal op amp, R3 has no voltage across it. Hence input voltage is Vs+2.5 .
* v+ = v- = Vs+2.5
* Since the gain is 1+ R2/R1 then this means that Vout = Vs+2.5 ( 1+ R2/R1)

**What I Know I got wrong:**

* The analysis above is only true for AC signals? But how could I do I arrive at the "general" answer for all types of signals. I am not sure how to approach this.