A.振幅为1,初相为π
B.振幅为7,初相为4/3π
C.振幅为7,初相为7/6π
D.振幅为1,初相为1/6π
[单选题]A.xyB.2xyC.D.xy+1
[单选题]A.B.C.D.
[单选题]A.36N·sB.90N·sC.64N·sD.81N·s
[单选题]A.B.0C.D.