sin θ·cos θ·tan θ<0,则θ属于()
A.(π/2,π)
B.(π,3π/2)
C.(-√2π/2,0)
D.(-π/2,0)
A.1←→2πδ(ω)
B.ejω0t←→2πδ(ω–ω0)
C.cos(ω0t)←→π[δ(ω–ω0)+δ(ω+ω0)]
D.sin(ω0t)=jπ[δ(ω+ω0)+δ(ω–ω0)]
A.cos(x^2)+2sinx
B.2xcos(x^2)+2sinxcosx
C.-2xcos(x^2)-2sinxcosx
D.2xcos(x^2)+2cosx
A.n*r*sin(3.14159/n)*r*cos(3.14159/n)
B.n×R×sinπ/n×R×cosπ/n
C.n×R×sin(3.14159/n)*R*cos(3.14159/n)
D.nRsin(π/n)Rcos(π/n)