3.如图,在四棱锥P−ABCDP-ABCDP−ABCD中,PA⊥PA\botPA⊥底ABCDABCDABCD,AD⊥ABAD\bot ABAD⊥AB,AB//DCAB//DCAB//DC,AD=DC=AP=2AD=DC=AP=2AD=DC=AP=2,AB=1AB=1AB=1,若EEE为棱PCPCPC上一点,满足BE⊥ACBE\bot ACBE⊥AC,则PEEC=(\frac{PE}{EC}=(ECPE=( )))