∴PD=PA？ PBPC=2。

Let de = X.

∵EA cuts ⊙ o at point a,

∴EA2=ED？ European community,

That is, x(x+8)=20,

x2+8x-20=0，

X=2, x=- 10 (negative values are discarded).

Then PE = de+PD = 4.