题目

     George Zimmerman's first court appearance before a Florida judge came on Tuesday in connection with the shooting of 17-year-old Trayvon Martin. The case has caused a national debate in the United States about race, self-defense laws and gun control.     It  was the first time the public had gotten to see and hear from George Zimmerman. The judge said he had found probable cause to move ahead with the case and told Zimmerman he would be formally charged on May 29th.     Zimmerman turned himself into authorities on Wednesday night, just before special prosecutor(检举（14分）如图，四棱锥P-ABCD中，PD⊥平面ABCD，PD=DC=BC=1,AB=2,AB∥DC，∠BCD=900 （1）求证：PC⊥BC （2）求点A到平面PBC的距离