good afternoon, I have question, on this number i find something very weird. when in the first equation we have equation about Vm. but when I substitute that equation in the second equation (opposite from the video lesson), I do not get the same answer for the video. why is it like that?

Vm= (V'm)+(2mV'2m)

(Vm)+(V'm)=0 +(V'2m) then it will be

(V'm)+(2mV'2m) +(V'm)= (V'2m)??