If PA = AAB (a belongs to R), then the trajectory equation of point Q (m, n) is? It's been a long time I hope I can write the steps clearly Especially the proof of straight line

If PA = AAB (a belongs to R), then the trajectory equation of point Q (m, n) is? It's been a long time I hope I can write the steps clearly Especially the proof of straight line

2OP=mOA+nOB
OP=m/2*OA+n/2*OB,
PA=λAB,
PA=OA-OP,
AB=OB-OA,
(OA-OP)=λ(OB-OA),
OA*(1-m/2)-n/2*OB=λOB-λOA,
1-m/2=-λ,
-n/2=λ.
m+n=2.
That is, q (m, n) trajectory equation is: M + n = 2