A.2sin4x B.2cos4x C.4sin2x D.4cos2x
答案:A
解析:(sin22x)′=2sin2x·(sin2x)′=2sin2x·cos2x·(2x)′=2sin4x.
5.函数y=的导数为_____________.
解析:令y=,u=.
则y′x=y′u·u′x=12·.
=12··.
答案:-12··
6.求下列函数的导数:
(1)y=(2x-3)5;(2)y=;
(3)y=ln(x+);(4)y=sin32x.
解:(1)设u=2x-3,则y=(2x-3)5由y=u5,u=2x-3复合而成.
由复合函数的求导法则,得y′=f′(u)·u′(x)
=(u5)′(2x-3)′=5u4·2
=10(2x-3)4.
(2)设u=3-x,则y=,u=3-x.
y′=f′(u)·u′(x)=()′(3-x)′
=(-1)
=.
(3)y′=·(x+)′
=[1+··(1+x2)′]