設y=cos(arcsinx/2),則y′(/2)的值等于()
A.-1/2 B.-/2 C.1/2 D./2
設,則k的值是:()
A.1/6 B.1 C.1/4 D.1/3
的值是:()
A.2 B.0 C.1/2 D.1/4