AP^2+BP^2+CP^2=(P-A)^2+(P-B)^2+(P-C)^2
=3P^2-(A+B+C)P+(A^2+B^2+C^2)
=3(P-(A+B+C)/6)^2+(A^2+B^2+C^2-(A+B+C)^2/12)
P=(A+B+C)/6