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3.已知四面体PABC中，点D,E分别为AB,PC的中点，若DE=xAP+yAC+zAB,则x,y,z分别为A.-1,11P2’2’-2E111’2A111C.-2’2’4D111BD.’2 4.在直三棱柱ABC-A1B,C1中，AA1=2...

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