let ABC be a triangle and let D,E be the mid points of the sides AB,AC respectively,then BE+DC=
OB = b vector
OC = c vector
OD= (a+b)/2
OE = (a+c)/2
BE = OE - OB ...solve it
DC = OC - OD .... solve it
BE+DE = 3/2 * (c-b)
BC= c-b
Therefore, BE+DC = 3/2* BC...
