
A.π/4
B.0
C.-π/4
D.π/2
[单选题]A.π/4B.0C.-π/4D.π/2
[单选题]A.π/4B.0C.-π/4D.π/2
[单选题]A.π/4B.0C.-π/4D.π/2
[单选题]A.π/4B.0C.-π/4D.π/2
[单选题]A.π/4B.0C.-π/4D.π/2
[单选题]A.π/4B.0C.-π/4D.π/2
[单选题]( )。A.B.C.D.
[单选题]( )。A.B.C.D.
[单选题]A.2/3B.7/9C.20/21D.9/14E.1/2
[单选题]A.2/3B.7/9C.20/21D.9/14E.1/2