在四棱锥 P−ABCDP - {ABCD}P−ABCD 中, ∠APB=∠BPC=∠CPD=∠DPA=60∘\angle {APB} = \angle {BPC} = \angle {CPD} = \angle {DPA} = {60}^{ \circ }∠APB=∠BPC=∠CPD=∠DPA=60∘ ,且 ∠APC=∠BPD,PB=PD,PA=6\angle {APC} = \angle {BPD},{PB} = {PD},{PA} = \sqrt{6}∠APC=∠BPD,PB=PD,PA=6 ,若该四棱锥存在半径为 1 的内切球, 则 PC={PC} =PC= ___.
