设伪球面x(φ,θ)=(acosφcosθ,acosφsinθ,a[ln(secφ+tanφ)一sinφ]) (a>0).证明:
A.-sin(x+y)(1+y’)=4
B.-sin(1+y’)=4
C.-sin(x+y)=4
D.-sin(x+y)y’=4
设x(t)和y(t)分别是平稳随机过程,若
z(t)=x(t)cosωot-y(t)sinωot
A.cos(x^2)+2sinx
B.2xcos(x^2)+2sinxcosx
C.-2xcos(x^2)-2sinxcosx
D.2xcos(x^2)+2cosx