(adsbygoogle = window.adsbygoogle || []).push({}); *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.

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# Homework Help: *sigh* volatage divider ?

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