これを先に求めた電位差の合計の式にいれると
V = V1 + Vbc
= V1 + (C1/Cbc)*V1
= (1+C1/Cbc)*V1
= (1+C1/(C2+C3))*V1
= (C1+C2+C3)/(C2+C3)*V1
よって
V1 = (C2+C3)/(C1+C2+C3)V