单项选择题
A.sin(0.7πn)B.cos(1.7πn)C.ej2.3πnD.e-j0.3πn
A.\delta[n]B.u[n]C.0.5n(u[n+2]-u[n-3])D.sin(0.2πn)u[n]
A.0.5<∣z∣<3B.0.2<∣z∣<0.5C.∣z∣>3D.∣z∣<0.2