问题 选择题
函数y=
sinx
cosx
的导数为(  )
A.
cos2x-sin2x
cos2x
B.
-cos2x+sin2x
cos2x
C.
cos2x+sin2x
cos2x
D.
-cos2x-sin2x
cos2x
答案

∵y=(

sinx
cosx
)=
cos2x-sinx(-sinx)
cos2x
=
cos2x+sin2x
cos2x
=
1
cos2x

故选C.

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