Non inverting amplifier :
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