Vector AP=(vector c-vector b)/2
Vector BQ=(vector a-vector c)/2
Vector PQ=vector PA+vector AB+vector BQ=(vector b-vector c)/2+vector c+(vector a-vector c)/2=(vector A+vector b)/2.
Vector AP=(vector c-vector b)/2
Vector BQ=(vector a-vector c)/2
Vector PQ=vector PA+vector AB+vector BQ=(vector b-vector c)/2+vector c+(vector a-vector c)/2=(vector A+vector b)/2.