Nodal analysis voltage confusion

[princejan7]

So the voltage across the R2 resistor is given as vT-0 = vT

But then the voltage across the R1 resistor is given as "vT-Vs1"
I'm not sure which two nodes the voltage across R2 involves. Is it the same as R1?

Also, I am not sure of the voltage source vs1. Across which two points does it apply?

 

[gneill]

Can you identify the nodes in your circuit? The diagram specifies explicitly where V_s1 is connected...