... ị P l trng tõm DSCM, Q l trung im ca MB. Ã MDPQMCNBVMDMPMQVMCMNMB1211 23 26 === ị DPQCNBMCNBVV5 6 = Ã Vỡ D l trung im ca MC nờn dMCNBdDCNB(,())2(,())= ị MCNBDCNBDCSBSABCDVVVV.122=== ... PT. Nhõn 2 v ca PT vi cosx, ta c: PT xxxx32sin3(4cos3cos)cos-= xxx2sin3.cos3cos= xxsin6sin2pổử=-ỗữốứ kkxx22147105pppp=+=+ 2) PT xxxx24233113-+=-++ (1) Chỳ ý: ... ị DPQCNBSABCDVV.512= ị SABNPQSABCDVV.712= ị SABNPQDPQCNBVV75= . Cõu V: T gi thit xyz2221++= ị xyz0,,1<<. Ã p dng BT Cụsi cho 3 s dng: xxx2222,1.1 ta c: Trần Sĩ...