Connecting AC, ∫pa⊥ plane ABCD

∴? The projection of PC on the bottom surface is AC

∴? ∠PCA is the angle formed by PC and plane ABCD.

In the right triangle PAB, AB=6√6, PB=6√ 10.

∴? PA=6*2= 12

In the right triangle PAC,

PA= 12，AC=√2*AB= 12√3

∴? tan∠PCA = PA/AC = 12/( 12√3)=√3/3

∴? ∠PCA=π/6

∴? The angle between PC and plane ABCD is π/6.