20.( 1) the focus f of parabola x 2 = 2py ① is (0, p/2), and the directrix l:y=-p/2 intersects with the y axis at e,

Circle f intersects l at b, d, ∠ bfd = 90,

∴FB=FD,BE=DE=EF=p，

∴FA=FB=√2p，

∴ circle f: x 2+(y-p/2) 2 = 2p 2, ②

Substitute ① into ②, y 2+py-7p 2/4 = 0, ya > 0,

∴yA=(2√2- 1)p/2，

∴s△abd=( 1/2)bd*(ya+p/2)=√2p^2=4√2，

∴p^2=4,p>； 0,

∴p=2, and the equation of circle f is x 2+(y-1) 2 = 8.

(2) The topic is incomplete.

23. The topic is unclear. Can you type it?