A.(1,-1,2) B.(1,1,2) C.(-1,1,2) D.(-1,-1,2)
A.连续 B.左连续,且不连续 C.右连续,且不连续 D.既非左连续,也非右连续
A.A=D或B=O B.BA=O C.(A+B.2=A2+B2 D.(BA.2=0
A.-x+y+z-4=0 B.x-y-z-4=0 C.x+y+z=0 D.x+y-z+2=0
A.(0,0) B. C. D.(1,2)和(-1,2)