*sigh* volatage divider....? I've been going over basic circuitry and got to the voltage divider. I don't understand the proof here: http://en.wikipedia.org/wiki/Voltage_divider#General_case The first line makes sense. From Vi to Ground there are two resistors in series, so you add them, and V = IR and I is the same all around the whole circuit. Then the 2nd line I don't get. Why is it R2 and not R1? I thought current would go From Vi through R1 and then to Vo, not Ground to Vo.