∵PA,PB为圆O的切线
∴PA=PB=6
∵切线EF切圆O于C,交PA于E,交PB于F,
∴BF=CF
AE=CE
∴△PEF周长
=PF+EF+PE
=PF+CF+CE+PE
=PF+BF+AE+PE
=PB+PA
=6+6
=12