Non-inverting Amplifiers

in the non inverting amplifers circuit , the negative inout (-) is connected to the Ground. and the input  Vg   is conected to the + (positive input) and thus it is obtained the same  phase between  input signal and the output signal.

 

since input empedence is too low we can say that lin = 0;

and then

and   no  current flows in the inputs , and we can take Vı =Vg 

-Vg.Rf=R1.(Vo-Vg) + Vg.Rf = 0 =>R1.Vo-R1.Vg+Vg.Rf=0

and then